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Slowing Down The Icarus Probe & Induced Deceleration
by admin
As part of the Project Icarus Terms of Reference, essentially our engineering requirements, the team is required to demonstrate some form of deceleration for the Icarus probe. The exact text stipulates “The spacecraft mission must be designed so as to allow some deceleration for increased encounter time at the destination”; note the phrase ‘some deceleration’. The exact amount was not specified but a 1% deceleration from the cruise velocity would probably be considered inadequate to meet the requirements. Possibly, a 10-20% deceleration would meet the requirements but this is a matter for team discussion and for the judgment of others who may view the design post-project. Ideally, the probe would be decelerated by more like 70-90% of the peak cruise velocity, but this is a real challenge to achieve. Currently, several areas of investigation for deceleration have been identified and these include: Reverse engine thrust, solar sail, Magsail, Medusa sail, microwave sail, orbital slingshot, aerobraking. These are briefly discussed.
Reverse engine thrust simply means using the same engine as used during the boost phase, but to decelerate the probe. However, there are several issues with doing this. First, this necessitates that the large mass engine (or a separate engine) must be carried by the probe into the target system, which minimises the staging potential. Second, the amount of propellant goes as the square of the mass ratio assuming an equal acceleration-deceleration profile, so the propellant mass would be increased to an unreasonable amount. Instead, one can go at a much slower cruise velocity and minimise the propellant mass required overall, but for a maximum mission requirement of 100 years this doesn’t allow for much margin.
But here is a quick back of envelope calculation using the existing Daedalus design and assuming its stage exhaust velocities. With a propellant mass of 46,000 tons (first stage) and 4,000 tons (second stage), and with a stage structure mass of 1,690 tons (first stage) and 980 tons (second stage), including the 450 tons science payload. If the vehicle undergoes its normal first stage acceleration for 2.05 years it will reach a cruise velocity of around 21,900 km/s or 0.073c where it will reach a distance of around 4,733 AU or 0.075 light years. But now rather than ignite the second stage, instead allow the vehicle to cruise at this speed for 41 years, until it reaches a distance of 3 light years, which is a total of around 3.1 light years when you add on the boost distance. Now use the second stage engine for reverse acceleration (deceleration) which takes just under 2 years (but we neglect this) and the vehicle will achieve a velocity increment of around 14,970 km/s or 0.05c, but in the opposite direction. Subtracting this from the cruise velocity already obtained, the vehicle now has a new cruise velocity of 6,930 km/s or 0.023c. Coasting at this speed it will reach the nearest stars 4.3 light years away in around 55 years from the end of the deceleration phase. This means that the total trip time to the Alpha Centauri system is just under one century, within the Project Icarus Terms of Reference. These simple numbers suggest that the idea is at least worth exploring further. Lets look at some of the other deceleration options being considered.
A solar sail will receive an intense flux of photons from the target star and thereby through momentum transfer decelerate the probe. However, in order for the sail to be effective it would have to be very large and be deployed near the target star. Also, there are concerns about a solar sail successfully unfurling and deploying after several decades of storage. In any case, initial calculations performed by the Icarus designer Pat Galea indicate that a sail for deceleration may not sufficiently slow down the probe. In work presented at the July 2010 New York Solar Sail symposium Galea showed that for a 50 ton probe travelling at a speed of 0.1c to perform the entire deceleration to a parabolic orbit capture using the sail alone, the calculated idea sail area would be seven hundred billion meters representing a circular sail of diameter nearly 1,000 km. Although one wonders what size of sail would be required for a much slower cruise velocity. Using the same data provided by Galea for 50 ton probe the sail diameter requirements become ever smaller for decreasing velocities: 472 km (0.05c), 377 km (0.04c), 283 km (0.03c), 189 km (0.02c), 94 km (0.01c) and 47 km (0.005c). For a sail of order 10 km in diameter, this would necessitate a cruise speed of around 0.001c. These numbers at least suggest further examination of the potential for solar sail deceleration is required.
A MagSail uses a magnetic field to deflect any charged particles radiated from the target star in a sort of plasma wind and use this deflection to impart deceleration to the main probe. The idea for using the MagSail in an interstellar context was first discussed in 1988 by the physicists Dana Andrews and Robert Zubrin in their paper “Magnetic Sails and Interstellar Travel”. The Icarus designer Adam Crowl has conducted some initial calculations which indicate that the deployment of this technology would be more useful when decelerating down from a higher velocity. This work is ongoing and shows good potential.
The Medusa sail uses the technology of nuclear explosion emitted from so called ‘units’, similar to Project Orion conducted in the 1950s and 1960s. The idea was first discussed in a set of papers published in 1999 and 2000 by the physicist Johndale Solem. Instead of using a large rear pusher plate to subtend a small angle as done for Project Orion (the shock absorbers of which also limit the performance), the Medusa sail utilizes a large sail (spinnaker) ahead of the probe, probably constructed out of a very high strength nanotechnology polymer such as aligned polyethylene. The detonations occur in front of the vehicle but behind the hemispherical sail so accelerating it and pulling the probe along. The cable line between the sail and the spacecraft is long, so that longer shock absorbers can be used which also (arguably) allows for an improved performance. A specific impulse of order 100,000 seconds is claimed to be possible for this propulsion system, where the velocity obtained from a single detonation increases for a larger caopy area and the closer the detonation point. The velocity will also be proportional tothe energy from the detonation and so the number of units used. The technology of a Medusa sail could similarly be used for deceleration of the Icarus probe, either by using direct nuclear explosions or even many inertial confinement pellets. Initial calculations for this concept are underway by the design team.
A Microwave sail is an alternative to a solar sail or direct laser propelled system. Microwaves are sent out using a maser. This concept was explored in a landmark 1985 paper titled “Starwisp: An Ultra-light Interstellar Probe”, by the physicist Robert Forward. Like the solar or laser sail, the microwave sail offers a rocket-less solution for an unmanned probe, where the wavelength of any microwave beam would be greater than the holes within the wire sail mesh that would constitute a Starwisp type probe. In theory, the Icarus vehicle could deploy a large number of Starwisp probes in the target system and decelerate them using an on-board microwave beam.
Orbital slingshot refers to the probe flying into the target solar system but performing several large flybys of the star and planets in order to gradually impart deceleration through momentum change. This is similar to how probes like the historical Pioneer 10 and 11 picked up velocity from the gas giants in order to leave the solar system. This method may be possible in the Centauri A and B system but it would be difficult to achieve in other star systems, especially considering the hyperbolic velocity of the probe as it enters the system. Potentially, such a probe could first visit Promixa Centauri and then gravitationally slingshot around to the Centauri stars. Proxima Centauri is around 13,000 AU from Centauri A and B.
Aerobraking refers to the probe entering the upper atmosphere of either a planet or the target star, skimming the surface, like a pebble on a pond, just enough to impart some deceleration on the probe. For a spacecraft moving a say 0.1c it is not by any means certain that deceleration by this method is feasible given the likely heat loads and some analysis by the team is required to consider whether any potential exists here, perhaps by multiple-planet hopping skips. Icarus designer Adam Crowl has recently suggested that a probe could perform a ‘fryby’ of Proxima Centauri with a very close pass and then be deflected towards Centauri A and B.
There appears to be several options for deceleration that the Icarus design team are exploring. One option however is that instead of adopting any one of the above is to adopt an element of each method in order to gradually impart deceleration to the main probe. Utilizing a hybrid deceleration system along with the adoption of a low cruise velocity ~0.08-0.09c (see blog article “Daedalus & Icarus: Flyby versus Deceleration”) would seem a sensible option to ensure that the probe can be slowed down to a reasonable velocity in the target solar system and thereby ensure that the encounter time in the system is at least many months. One scenario would see the probe gradually slowed down by the use of a MagSail as it approached the target system and then a Medusa sail could be deployed to decelerate further still. On approaching the solar system, a laser/sail deceleration of a sub-probe could be deployed, perhaps accompanied by later engine burn to bring it down into orbital velocity. A complex set of manoeuvres for a presumably autonomous probe several light years away. But perhaps what is really needed for the ‘deceleration problem’ is some out of the box thinking, hence the concept of induced deceleration.
To induce something is to bring about or stimulate the occurrence of it. In the context of Project Icarus, Induced deceleration refers to the artificial creation of a desirable physics phenomena that doesn’t otherwise exist naturally in a sufficient amount or magnitude. The Starwisp is one example of this in fact, because the microwaves don’t exist naturally in sufficient abundance, so instead the vehicle carries along its own maser beam. Another example of induced deceleration is to create an intense particle flux field which impacts the probe shield and imparts momentum. This would be achieved by firing a projectile into an asteroid or comet ahead of the main probe, although assuming an isotropic debris field the probe would only receive a fraction of the explosion, hence the impact would need to be closely timed for maximum effect. Another example would be to detonate a large energy device inside a dense molecular cloud, causing the generation of a shock wave which the main probe then fly’s into and undergoes some drag. A sub-probe could also be launched ahead of the main probe when ready and deploy a laser (or maser) to irradiate a large sail which has been deployed on the main probe, in the absence of sufficient natural solar irradiation. The principle of induced deceleration is to identify the deceleration option and physics effect required, then assess if its available naturally in a sufficient amount, if not create it artificially using the on-board technology.
Another idea worth exploring was (possibly) first suggested in1976 by Robert Forward in his paper ‘A Programme for Interstellar Exploration’. Forward suggested that the x-rays from a fusion engine could be captured and used to pump an on-board laser system which could then be used for additional thrust. Project Icarus could adopt such a scheme but for the use of deceleration. This would be another example of induced deceleration, where the laser could either be used directly as a photonic rocket or used to impinge upon any deployed solar sail surfaces on a sub-probe. Designing this system would not be an easy challenge, but its certainly worth exploring further by the Icarus design team.
Quite possibly, deceleration represents the biggest technical challenge for the Icarus design team to solve, hence all ideas are welcome on the table and readers are invited to submit their suggestions to this article. This would be a valuable contribution to the project. In a recent email to this author, the renowned author and physicist Greg Matloff (also a Project Icarus consultant) commented that if the Project Icarus Study Group could solve the deceleration problem, this would justify the initiation of Project Icarus in itself. The challenge is on then, for the design team to come up with some credible answers.
Why thinking of decelerating the entire ship ? Think broader ! We could decelerate only a VERY small part of the ship: imagine the ship is carrying a magnetic rail gun that would be used to propel a very small “bullet” in the opposite direction of motion : that bullet would then have a very small relative velocity with respect to the star, and perhaps it could even land on a planet : because it is very small, it would not suffer too much from crossing the exoplanet atmosphere. And, thanks to miniaturization, it could contain a camera and a transmitter, or even a nanotech-engineered factory of replicators, that would use the local material to build a whole set of exploring devices ! See eg
http://sboisse.free.fr/technique/voyage_interstellaire.php
(in french, sorry
Serge,
We are looking at the possibility of decelerating only part of the vehicle, a sub-probe. We are also thinking about other ideas like Starwisp probes and needle probes, the latter of which is similar to your suggestion. But we should give this more thought. Any other ideas on deceleration please post – we want idea – lots?
Kelvin
Hi serge
Any idea how big the rail-gun would be to slow from 0.1c? But the basic idea is not unreasonable. One of our investigators is examining using microwaves to brake sub-probes along the lines of Robert Forward’s Star-Wisp.
Well, PJMIF concepts that have been explored contain up to 32 powerful railguns (for interplanetary missions, Icarus would likely use more) , which could be modified for use of launching “useful bullets” other than the fuel jets.
Another thing that I think we should actually analyze in more detail is how much weight can we actually save by introducing better materials, more advanced propulsion etc. If we could make a large percentage savings on overall mass (primarily on better radiators and capacitors), then we could maybe put in some additional fuel for deceleration.
Hi Milos
How fast can the railguns fire a mass? How fast do they accelerate a plasma “bullet”?
Well, for now, Hyper-V made plasma go out within a range from 10 km/s to about 100 km/s I think, depending on the mass of course. Mass wise, we’re talking tens to hundreds of micrograms. Hyper-V and Dr Francis Thio are confident this could be significantly larger, but our funding is kinda limiting the possibilities currently. Some of the PJMIF concepts that I’ve seen extrapolate that up to 500 km/s in the fairly near future. Not really a significant portion of c, but better something than nothing.
Hi, Kelvin et al. If your ship is accelerated by any kind of rocket engine, then I don’t see any problem with using reverse thrust to slow down at the other end, and I don’t see why in the “back of the envelope” example you give you want to decelerate a full light-year before you reach your destination. Surely you want to decelerate to less than the star’s escape velocity just as you are entering its planetary system, say 50 AU out?
Anyway, the basic arithmetic is that if any rocket-propelled starship can get to a particular star in a certain time _without_ decelerating at the other end, then it can make the same journey _with_ deceleration if it takes double the journey time (plus a little bit more for the deceleration manoeuvre itself). Thus the same design can serve as a flyby probe, a slow flyby probe or an orbiter just by reprogramming the engine burns.
You could even launch the probes in pairs: one burning all its fuel to accelerate and get a quick initial look, while its twin saves half its delta-V for deceleration and in-depth studies after arrival.
Having said that, I do recall that Daedalus would not have been able to stop at Barnard’s star by doubling its journey time because the fusion reaction is triggered by doping the fuel pellets with tritium, whose half-life of about 12 years means it would have been past its use-by date by the time of arrival!
Stephen
Hi Stephen
Braking from ~0.1 c in just 50 AU means a braking deceleration of ~6 gees and so isn’t a very practical performance target for a fusion rocket.
Adam, I meant: braking in such a way as to slow down to below escape velocity in the destination system when ~50 AU distant. Obviously, such a braking burn will have begun a couple of years earlier! So the acceleration and braking burns would be roughly symmetrical.
Stephen
If the purpose of deceleration is to increase the amount of observation time then why not just detach a whole line of small subcraft toward each target exoplanet in the system without having to decelerate them at all? So, instead of having one second of flyby time, 100 subcraft gives you 100 seconds. You could also image both sides of the planet. By spacing the line of subcraft in time you could have them autonomously identify potentially interesting characteristics, communicate that to later (perhaps larger, more sophisticated subcraft) for more focused and detailed observations. Although this approach doesn’t involve deceleration, it accomplishes the same goal.
good to hear from you John.
But what about the velocity? as we deploy each subcraft they will have the same speed as the main vehicle and will just continue to match it unless you decelerate each one.
Kelvin
Kelvin and John,
The purpose of deceleration is to bring the vehicle into astrocentric orbit in the destination system, from where it or its sub-probes can move to planetocentric orbits around each planetary and satellite body in turn.
One of the most interesting scientific investigations, from the point of view of both science itself and the wider society stumping up the money to pay for the exploration, is the search for life, and observation of any living organisms found. This absolutely requires the starship to carry landers which can give us ground truth on worlds analogous to Earth, Mars, Titan etc.!
Incidentally, since the first target will certainly be Alpha Centauri (unless a close Earth analogue is found orbiting Barnard’s Star or another very nearby star), Icarus must be designed with a double payload from the outset, of which one unit goes into orbit around the A star and another around the B star (and maybe one for Proxima as well?).
Stephen
Hi Stephen
Depending on what auxillary propulsion system is chosen, or if a maneuver tank is retained (like “Daedalus”) then the Main Vehicle may be able to visit both stars itself. A sub-probe for Proxima or a high-speed but partially decelerated flyby would be highly desirable.
The logistics and timing get pretty hairy, but something similar to John’s idea with multiple phases of “swarming probes”. By the time the system is reached, the ship is just the original propulsion and most of it is now a scattered swarm. This only works though if passive slowing of smaller masses gets substantially more practical.
A portion of the ship is detached without any slowing to then advance scout the system (the issue is timing as the advance will relay back to the main ship, then earth, then any decisions need to be sent again). This could be multiple advance scouts to observe all objects in the system and identify all targets for further observation. (Turning it into a multi-phase mission)
After scouts are released, the main ship is already decelerating somewhat using whatever option works best for the large scale and high speed. Smaller probes would be launched with semi-redundant missions and different deceleration strategies.
The small probes have the issue of actually transmitting back to earth, so separate comm links would also release?
Just from following the progress in satellite and probe design, basic probes are getting smaller and cheaper. Although not attractive for efficiency, a scatter shot strategy of simple tiny probes could be viable. If costs come down as is being seen, producing 10,000 semi-redundant miniature probes would have minimal cost compared to this overall mission. They could collect a wide range of information and use a more substantial comm relay. This would also allow for more high-risk deceleration methods with some acceptable loss rate.
Kind of stream of consciousness, but I think it makes sense.
Garrett
Slow down the sub probes?Easy!Launch them out the back[railgun?] That oughta make them slower.Hope I didn’t waste my time in GED classes!
Could decelerating using the regular solar sail method (and light/solar wind) be made more effective by somehow provoking the target star into creating more solar wind as you get closer? Don’t know if it is possible to affect the star’s output efficiently enough in a focused-enough burst that it could be aimed back at yourself, kinda like generating your own headwind. Any energy/mass we fire at the target star also slows us down too.
PS liking the multiple-small-subprobes which can much more easily decelerate, and if enough of them are there maybe not even need to decelerate much for many of them/the early ones.
Others/Garrett, remember there is no decision-making communication with the earth when you’re close to the target star; on the way yes, for updates/plan details/minor changes or corrections when you’re far enough away that the yrs of round trip for messages isn’t an issue. But we can’t make short-term decisions for it when its almost there.
Thinking about the starwisp idea.
Launch maser ahead of starwisp, then launch your starwisp.
When the time has come to slow down to enter your destination star system, go to your maser, turn it on and go back home. The maser will slow down the starwisp(s) to go into orbit and the maser could enter the star it self (the idea is to point it straight at the star, use solarcells to power it) or use iec fusion reactor.
Has any-one started to evolve an interactive and collaborative Google spreadsheet so interested parties can assess different scenarios, question the assumptions etc?
(If some-one could point me to the relevant equations and assumptions, I could initiate something myself.)
Hi Rod
That’s a very good idea. We might just do that.
Roland, the maser would need to be very large to deccelerate a Starwisp – so much so that launching the maser would mean we could do without Starwisp probes.
hello, from my understanding for a magsail and a solar sail is that they take up vary little room when stored and are light, what i prepose is several sub probes with a sail made from the 2 systems combined into one sail and as the sub probes would be small and light and would not need any power for the sails to work each one having its own sail and once the probes have slowed down enough they could disconect there sails or refold them and then form some form of aero breaking to bleed of the last of probes speed im not sure if that would remove all of the kinetic energy needed but i thought it was a good idea
Hi Hugh
That combined concept is under study. Thanks for your interest in Project Icarus!
I see mention of atmospheric drag induced deceleration, but only in context of ‘dipping’ the craft into a planetary(/solar) atmosphere. Why would you dip the entire craft when you could use a drag line? If the craft deployed some sort of robust tow line with an appropriately designed ‘bucket’ or ‘chute’ on the end you could probably ablate it to death and then just deploy another one. If the ‘bucket/chute’ were appropriately designed then you could leverage more than just the ablative properties of the ‘chute’. Assuming your target drag atmosphere were gaseous and composed of the correct elements, you may even be able to build the ‘bucket’ to be a mass accumulator. This way it as it ablates, and drags it gets heavier…fills up and compresses atmospheric gases. Like a greedy little ramjet. Do this enough, or maybe to a star (large mass) and I bet you could net some nice newtons.
Well in theory traving at 0.09c is far easier than traveling at 0.1 c due to relatvity. Performing a fryby will probably destroy the craft or at least part of it. Aerobraking may do the same to. One good option is the magsail which takes advantage of the plasma that you are traveling through. You also have the option of decelerating entirely using the engines but that will require more fuel. Any way you decelerate you will have to use the engine for part of it.
This concept of accelerate for 4 years, coast for 30 or 40, then slam on the brakes for a few years seems like the way some people drive between stop lights. For one thing, it requires a large, heavy engine. Would it not be better to accelerate slowley over 30 or 4 years with a lighter engine, then turn around, and spend the rest of the time inbound decellerating to the desired encounter speed? Decreace the collective weight of the engine or engines, and you decreace the amount of fuel requried (which further decreaces the amount of fuel required to move that fuel). Seems much more efficient way to get there in the same amount of time.
Sorry, it should say “30 or 40 years” above.
Kelvin, just wondering if you guys had come up with any ideas in the couple months since the last post?
What about a modular approach?
After initial acceleration is complete, detach the main engine and heavy fuel pods as stage 1. Maneuvering thrusters would direct stage 1 toward AB for an eventual fly-by at full speed, say .09c. While the command module is still years away, scanners on stage 1 report back to earth with initial survey data.
Using maneuvering thrusters after separation, direct stage 2 and the command module toward C. Use the stage 2 engine and fuel for a partial deceleration before reaching C, for an approach velocity of .06c. Use C as a slingshot to redirect stage 2 and the command module toward AB and shed a little more velocity.
After the slingshot, detach the secondary engine, fuel pods, and maser as stage 2, and unfurl the starwisp net from the command module. The stage 2 module, crusing toward AB at ~ .05c (maybe lower, I’m not certain of the degree of deceleration you can achieve with a gravity slingshot) directs its maser at the command module and starwisp, causing that unit to shed more velocity. If a solar sail can be deployed with the starwisp, the approach to AB can get some additional deceleration. Scanners on stage 2 allow a final survey of the system and help the command module plot a final-approach course.
Finally, detach the command module from the starwisp unit. The command module uses AB for another gravity slingshot maneuver, with any luck being in a position to use both stars.
The best way might be to find a way to utilize the resources in the target system. Imagine for instance that the ship comes equiped with a maser sail as indicated above. We could launch a couple hundred micro satellites that instead of decelarating, would simply break way from the ship and go into orbit around the star. Then they could collect solar energy, and then shoot it at the sail to decelerate it. They could be launched long before they arrive, and accelerated by a maser located on the ship itself. (this action could also help decelerate the ship a bit as well). They nano-satillte masers could be nothing more than a solar panel, attached to a maser and small circularizing kick motor. Done right they should arrive in orbit of the star a few years ahead of the ship. Then they could simply farm the star for solar energy, which is then used to power the deceleration. I’m not sure how viable this would be, and i’m not a scientist, but the more weight “outsourced” to our destination, the better. A modular approach with hundreds of small satelites working in concert would also act as a hedge against individual systems failure. Having anything complex sitting on ice for 60 years before we use it is an under appreciated problem!
The most out-of-the-box thing to do , is to rejeckt the way the problem is defined : Why exactly is it unquestionable that a deceleration have to be achieved at all ? If we are talking about an information gathering probe , and not YET a creewed starship , it might be easier and cheaper to devellop a probe capable of doing its task in a very short time . While zipping through the system with relativistic speed ,it must be capable of recording gigantic amounts of information in avery short time by using a great number of istruments simultaneusly,and by splitting itself up in several units to get additional wievpoints . All this recorded information could then be sent back to earth at a much, much slover pace ,using energy and masseffcient longwave frequency comunication . The part of the probe reaching the targetstar might weigh just a few tons, making the whole project possible many years earlier.
What if we develop a spaceship that splits itself into dozens or even hundreds of modules, each of which carries its own electric sail. The limiting factor for electric sails is their length. By having dozens or hundreds of electric sails, you could have a lot more deceleration than a single one. Also weight won’t be a problem, because electric sails are just made of thin wires, and not an entire surface. So even a hundred of them instead of just one won’t increase the weight by much.
Probes are wonderous. Take for example earths first interstellar probe, Voyager 1. Yes it took some happy snaps of our planets early in its life which were wonderous in their time. And now, 35 years later, still alive its crossing the boundary between our system and interstellar space where it seems great things are occuring. The Heliosheath, magnetic bubbles, Termination shock, and lately The Magnetic Highway. I think, from earths 1st probe the answers to your breaking problem may lie, and THIS year 2013 we will find out what IS outside our system… Watch this space.. http://www.nasa.gov/mission_pages/voyager/voyager20121203.html
So perhaps sails become parachutes and a craft surrounded in a magnetic field opposite to that of the oncoming magnetic field of the system you are entering. The Microwave Net sail spoken of may become a magnetic parachute. Interstellar space may have its own magnetic field which could be used for years of both acceleration and deceleration, and we will find out in the next couple of years as Voyager1 enters interstellar space. I just hope it can still call home through that magnetic outer barrier surrounding our system. And what of a craft travelling at 0.1c ENTERING a system through this region?
Whatever system is chosen, it must be able to have enough deltaV (either through stored fuel or the ability to do momentum exchange with the local medium) to change course and manoeuvre in the target system, or the utility is vey limited.
This means sails, in practice. The boost and interstellar cruise can be done using any sort of engine, but a magsail deployed soon enough could bring the effective velocity to 0, then the crew can use the magsail in order to carry out a survey,
Have you considered a self-cannibalistic propulsion system? Laser ablation and/or ion thrust come to mind. The idea here is instead of burning fuel (alone) or accelerating mercury ions (alone) that your engine also consumes the fuel tank and its supporting structure. Note, this engine could also consume a solar sail as well as anything else deemed unnecessary at that point of the mission. In the initial article description (first blog post), second stage was estimated at 4,000 tons fuel + 980 tons stage structure mass inclusive of 450 tons of payload. A self-cannibalistic propulsion system may save 500 tons at end of deceleration phase.
When someone writes an article he/she retains the plan of a user in his/her brain that how a user can know it.
Thus that’s why this piece of writing is outstdanding. Thanks!
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