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Rakaydos

Kerbal 2- Phobos Mission (Future Cubesat feasability study)

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This thread is for one of the popular missions selected by the KSP Cubesat mission poll. While unlikely to be flown on the first launch, I feel that laying the groundwork, the mission profile, and the vehical design will not only be useful for this mission, but give the LEO cubesat team something to practice.

The mission has several requirements, most of which are financial bariers. For the purpose of this topic, however, we are ignoring financial concerns. (within reason- no dedicated GTO flight, no RTGs, must fit the u3 cubesat profile, ect)

I believe the order of discussion should be:

Orbital Profile- the mission as plotted by K2 calls for a GTO launch, moon flyby, an earth flyby, a mars aerobreak, and phobos landing. But it's unlikely that we can find a "perfect" GTO carrier, so figuring out how to loiter to get the best launch angles will tell us D/v requirements and mission duration, which in turn will inform us on how much rad shielding, heat shielding, fuel, and TWR the cubesat will need. It will also inform what science is possible, how powerful the radio will need to be, and other concerns. (For instance, the difference in orbital period between GTO and LTO can fine tune our lunar flyby based on the launch profile without costing us any D/v we wernt already spending)

Vehical design- knowing what the craft needs to do, fitting it into a u3 chassis is the next task. Off the shelf components are nice but not nesssary- for the purposes of this thread an eager university student can hand-coil whatever ion drive specs we decide we need, as long as we can give them a solid blueprint. While preliminary studies say 1500 m/s Dv and a 2 year flight plan, that's assuming a best case launch- we should probably allow for some leeway to line up a proper orbit from whatever GTO ride we get on.

Science payload- This is what grant money is provided by. The weight and size will be limited by the u3, and by the other essental systems of the craft, but some science can be done by repurposing those essential systems.

Edited by Rakaydos

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"Within reason" - that would include Mars aerobraking and landing on Phobos. Because those are just insane and ridiculous notions.

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This whole mission is ridiculous. It's hard to just single out one part of it that's more preposterous than the rest. To aerobrake, you need a heatshield, which adds weight. You need a way to precisely control trajectory and orientation over months of successive orbits, so you need a way to communicate with the spacecraft and determine its orientation in space. Since we're talking about high Isp engines, we're probably considering some sort of ion propulsion, which means long non-impulse trajectories and a dedicated ground team to monitor and control the spacecraft's... ah whatever. It'll actually be pretty interesting to see the mission profile. That would be cool, regardless of whether it's actually feasible.

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First: "aerobraking" with actual satellites does not normally mean what it does in KSP; it refers to having an elliptical orbit which dips not very far into the atmosphere, which lowers apoapsis over hundreds of orbits. Aerocapture is using the atmosphere to go from hyperbolic escape orbits to elliptical orbits, and has never been done with interplanetary craft (skip re-entry has been done on Earth, which is sort of similar, but that was from a lunar return and not an interplanetary trajectory). To do an aerocapture, you not only need a very good heatshield system that probably needs to provide a lot of lift as well (to control g-forces), you also need to be able to do it within extremely precise tolerances, and you only have one shot to do so (during which you effectively cannot control what the satellite is doing; the onboard control system needs to be independently able to control the capture maneuver).

Edited by cpast

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Price within reason, not nessesarally objectives within reason.

But if aerocapture is off the table, how much would that add to the required Dv? 1000ms or so? Versus, say a 3 cm square of titanium for an expirimental aerocapture maneuver?

If solar cells cant cut it, has anyone looked into "BetaBatts" betavoltaic power cells?

We dont have to actually build this thing... we just have to prove it can be done. Solve each problem as it comes up, then solve the next one.

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Aerocapture may not actually be entirely off the table as a possibility (except due to engineering constraints): I had been going off of Wikipedia, and was unaware that landers have done direct atmospheric entry to Mars from interplanetary orbit. Still hard, but similar things have been done :P

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Can someone find the range ee would need to hiit for an aerocapture? Whats the weakest dv change ee would need to avoid going back to interplanetary space, vs the greatest Dv change without crashing on mars?

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Price within reason, not nessesarally objectives within reason.

But if aerocapture is off the table, how much would that add to the required Dv? 1000ms or so? Versus, say a 3 cm square of titanium for an expirimental aerocapture maneuver?

If solar cells cant cut it, has anyone looked into "BetaBatts" betavoltaic power cells?

We dont have to actually build this thing... we just have to prove it can be done. Solve each problem as it comes up, then solve the next one.

I think areocapture is still the best option, you could either waste tons of money trying get a propulsion system that has enough delta-v and can fit in a 3U cubesat, or you can try to get a heat-shield and control system that can do the areocapture.

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Mars Reconnaissance Orbiter had no heat shield when it did it's aerobraking.

It repeatedly dipped into Mar's atmosphere over six months and went from a 35 hour elliptical orbit around Mars to a two hour nearly circular orbit.

Well it must have used some fuel for the Mars capture.

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Mars Reconnaissance Orbiter had no heat shield when it did it's aerobraking.

It repeatedly dipped into Mar's atmosphere over six months and went from a 35 hour elliptical orbit around Mars to a two hour nearly circular orbit.

Well it must have used some fuel for the Mars capture.

MRO did a capture burn. The only craft that have entered atmosphere at escape speeds (i.e. on a transfer orbit) have been rovers. "Aerobraking" isn't actually used for this, the term is "aerocapture"; "aerobraking" refers to things like MRO, that do capture burns into a highly elliptical orbit and gradually lower apoapsis by dipping a tiny bit into the atmosphere over hundreds of orbits.

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I think the biggest problem with this mission profile is finding a carer who is launching into GTO at the correct earth mars phase anlge, and a the correct time such that we get a lunar intercept. Thinking about it this way we need a launch that launches within a couple of hours of when we want and no more than a few days either side of when we want. I think as cube sat we won't get this.

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It might be possible to do an Interplanetary Transport Network transfer, if we can navigate the craft precisely enough. That would eliminate the need for aerocapture, and may make it possible to get to mars without having to hit a precise window, any launch that can get us to a lagrange point will do the job.

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Once again I feel myself supported in my oppinion that KSP has the sad effect of downplaying the challenges of actual space travel.

Sounds like you want Orbiter then. KSP is a space program game, not a simulator. It should downplay the actual challenges because fun.

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Sounds like you want Orbiter then. KSP is a space program game, not a simulator. It should downplay the actual challenges because fun.

Shooters teach you more about shooting than KSP teaches you about space flight.

^ They should have a sticker like that on a loading screen.

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Shooters teach you more about shooting than KSP teaches you about space flight.

^ They should have a sticker like that on a loading screen.

They really don't, though.

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They really don't, though.

You see - that's exactly what Klingon Admiral has been talking about. You think that they don't, when in reality: they do.

I can't really give you any empirically verifiable proof of that, but let me put it this way: I knew more about shooting from playing BF3 then you will about space flight from KSP.

Edited by Sky_walker

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You see - that's exactly what Klingon Admiral has been talking about. You think that they don't, when in reality: they do.

No, they don't. KSP reflects how actual orbital mechanics works. It downplays *engineering* challenges, but orbital physics is reasonably accurate; rendezvous works the same way as in reality, for example. In contrast, shooting games have literally nothing to do with actual shooting in any way.

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No, they don't. KSP reflects how actual orbital mechanics works.

No, it does not. There are SoIs, magical atmosphere borders, no gravity gradients or effects of magnetic field, no reentry heat, no drag.... and that's just a beginning.

rendezvous works the same way as in reality, for example

Not really, though if anything is roughly similar in real life to KSP - it's rendezvous.

In contrast, shooting games have literally nothing to do with actual shooting in any way.

Well, there is recoil in (though you obviously don't feel), reload animations tend to be based on real weapons, switches on guns are in a correct positions, crosshairs look similarly.... when you'd compare percentage of knowlage you get from BF3 to real skill in shooting say: M16 and then compare KSP to real skill in, say: controlling a cube sat - BF3 would look like an ultimate simulator.

And besides - people playing BF3 know that it's BS shooter, while people playing KSP think that they actually know stuff about space flight. That's by far more dangerous and stupid. As our recent "KSP CubeSat" topic has perfectly shown beyond any shadow of doubt.

Edited by Sky_walker

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I think the biggest problem with this mission profile is finding a carer who is launching into GTO at the correct earth mars phase anlge, and a the correct time such that we get a lunar intercept. Thinking about it this way we need a launch that launches within a couple of hours of when we want and no more than a few days either side of when we want. I think as cube sat we won't get this.

This. All of those tracking problems is useless when we couldn't even launch at the right time

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No, it does not. There are SoIs, magical atmosphere borders, no gravity gradients or effects of magnetic field, no reentry heat, no drag.... and that's just a beginning.

Patched conics are sufficiently accurate to be used in mission planning when not near SoI boundaries. SoIs are not approximations invented by KSP, they're from astrodynamics, and when not near the boundary of one, you aren't losing *too* much accuracy by ignoring all other bodies. Atmosphere borders, valid, but not important over short timescales at typical orbital altitudes. Gravity gradients - not relevant for small craft. Magnetic field - not ordinarily relevant for orbital mechanics. Re-entry: that's not orbital mechanics. Drag: You mentioned it with "magical atmosphere borders", and are now repeating yourself (drag deep in atmosphere isn't orbital mechanics).

Not really, though if anything is roughly similar in real life to KSP - it's rendezvous.

How "not really"?

Well, there is recoil in (though you obviously don't feel), reload animations tend to be based on real weapons, switches on guns are in a correct positions, crosshairs look similarly.... when you'd compare percentage of knowlage you get from BF3 to real skill in shooting say: M16 and then compare KSP to real skill in, say: controlling a cube sat - BF3 would look like an ultimate simulator.

So, your argument for a simulator is based purely on aesthetics? It has nothing to do with the behavior of things ingame, and is just "does this graphically resemble the real thing"? Playing shooters has literally nothing whatsoever to do with actual marksmanship, which depends largely on physical control of the rifle (which shooter games do not simulate at all, since it's point-and-click).

Edited by cpast

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So, your argument for a simulator is based purely on aesthetics? It has nothing to do with the behavior of things ingame, and is just "does this graphically resemble the real thing"? Playing shooters has literally nothing whatsoever to do with actual marksmanship, which depends mostly on your control of the physical weapon (which shooter games do not simulate at all, since it's point-and-click).

Not aesthetics - actually giving you some rough idea what is where and where to put the things. If someone cares enough - he might even have some very rough idea on how to hold a weapon (one of they guys I know instinctively held the gun right, instructor was surprised, but all the experience he had was from playing BF3 and some other random shooters).

And to use your comparison - your argument for KSP being a simulator is based purely on aesthetics? Orbits in LEO cases look like they are in a real life, but playing KSP has literally nothing whatsoever to do with an actual control of the space ship, which depends on so many factors and elements that there are hundreds of people hired to take care of it all.

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We're getting off-topic, I think. Back to topic: How likely is it that you get launched within the narrow window of the ITN?

Edited by cpast

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