Kerbal 2- Phobos Mission (Future Cubesat feasability study)

[Rakaydos]

Agreed. There is plenty of fun in designing a mission and then challanging the eggheads to do it in our place.

[Rakaydos]

So, from a feasaility standpoint, Lunar flyby just needs a GTO carrier and a few hundred Dv. Science is limited to stand-off instraments- visual imagry, possibly laser spectrography. More ideas appreciated.

For beyond the moon, what range of Lunar angles can we, (with a perfect lunar insertion) get a solar semimajor axis of 1 AU? (I expect this will be limited by the lunar surface on one extreme, but what would that angle be, and what is the other angle, where we fail to leave earth's SoI/never enter the moon's SoI at all?) Some angles will require more DV from GTO than others, of course, but I want a hard look at the how different lunar slingshots can generate the possibility of an exact 1 year flight time. Science for a solar orbit is a question of command and control endurance outside earth's magetosphere, possibly a first for such a small craft. Any other science we do would pale in comparison, I believe- the very thing that makes this so hard is why it is so interesting scientifically.

Once returning to earth's SoI, we can aerocapture in the upper reaches of the atmosphere- we wont really have much interplanetary velocity so we dont need much aerocapture Dv at all. A basic heat shield, and a record of flight instriments is again all the science we would need, as we would be pushing new boundaries.

Once that trinity is complete, we can look at the sequal- the earth slingshot, a mars aerocapture from earth control, and the phobos orbit/crash/landing.

[Sylandro]

I'm going to try to contact NASA to see if we can make this happen. Meanwhile, i'm going to do the mission in KSP tomorrow.

[Rakaydos]

I'm going to try to contact NASA to see if we can make this happen. Meanwhile, i'm going to do the mission in KSP tomorrow.

Has to be RSS or it doesnt count. also the launcher you use has to deploy something else in geosynch orbit, to calibrate the misson properly- since we're depending on a Geosynchronus Transfer based launch orbit.

[Sylandro]

Has to be RSS or it doesnt count. also the launcher you use has to deploy something else in geosynch orbit, to calibrate the misson properly- since we're depending on a Geosynchronus Transfer based launch orbit.

Nah. I've had a really bad experience with RSS, so no.

[jfull]

Even if the community could get close to getting this to work, we'd still need some sort of mission control

[Rakaydos]

Even if the community could get close to getting this to work, we'd still need some sort of mission control

If we get that far, I'd be willing to bet we can borrow something.

Personally, I'm looking at this less as a kerbal forum mission, and more as a kerbal forum presentation to the Cubesat Community- "We could totally do this if we had a million dollars! (and a ride) Really! Here's how!"

[Mazon Del]

Hey guys....I just had a fascinating idea....it is a rather large long shot. UAE recently announced they planned to send a probe to Mars by 2019...One thing I noticed when I was eagerly watching the progress of Curiosity on its way to Mars was that they spin the craft to keep it stabilized on its path, and one thing they do to help keep the craft balanced during the spin is, you guessed it, ballast! The very thing that cubesats replace on normal rockets to get rides into space. Considering they just announced that they were doing this, they likely have not committed to much as far as craft design goes. Clearly we would need to involve UAE citizens in the process, but I can't help but wonder if it might be possible to convince them to use US as ballast. If we did it and the UAE made their timeline, we'd beat the MIT team there! (As a student from WPI, I am in favor of thumbing my nose at MIT, for fun of course. ). Any UAE citizens lurking around?

[Rakaydos]

But... but that's CHEATING! *agast*

[Aghanim]

Has to be RSS or it doesnt count. also the launcher you use has to deploy something else in geosynch orbit, to calibrate the misson properly- since we're depending on a Geosynchronus Transfer based launch orbit.

First we need the KSPTOT to work with the RSS. Then we can do the trajectory planning.

[Mazon Del]

But... but that's CHEATING! *agast*

Not really. ^^ Cubesats are already used as ballast on rockets up to orbit, why not being used as ballast on the way to elsewhere?

Thinking about it even more, what would be really funny, is if the stars aligned and not only did we get the UAE to give us a ride, but our radio wasn't designed to transmit back to Earth, it instead used the NASA satellites as relays. So we'd need to get NASA's permission.

[Rakaydos]

Best part, the off-the-shelf 8051 costs $10. So we can burn through a stack of them during development and testing without costing us. On the other hand, I've found rad-hard version of the same chip (UT69RH051) for $1,275. Expensive, but it's the sort of funds we might even find at the last possible moment, and still be able to swap out the off-the-shelf 8051 for a rad-hard one.

The UT69RH051 seems like the best chip for the Solar Orbit mission, and is our first hard price tag we can put on our "advanced mission."

We still need to price the ion drive and the power source- almost everything else, we can manage in the software or cobble together from spare parts.

[Mazon Del]

For the ion drive you might want to look at that MIT team that is working on one for their own Mars mission. Maybe they'd be willing to build one if we paid for it, though I would assume it would be quite expensive.

[Skyler4856]

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

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

Oh, yeah, I remember the time I shot 20 rounds per second without breaking my arm, good times, good times...

[Rakaydos]

Check my math here. Assuming everything else goes to plan. We get a GTO launch, we lunar slingshot into the correct orbit, the computer survives a year in solar orbit, we get the mars intercept off the earth slingshot, we aerocapture at mars, and nail the phobos transfer orbit.

Can we land?

Phobos has a surface gravity of 5.7 milimeters per second per second, according to the nasa page. Fully fueled, our cubesat will weigh no more than 4 Kg- less, after burning to Lunar transfer Orbit and making course corrections.

To have a TWR of 1.0 when wet (and thus >1 when it reaches phobos), by my math we will need 22.8 milineutons of thrust.

According to the Ion drive wiki page, that is well within the capability of an ion drive... if we can give it something on the order of a Kilowatt of power.

The largest expanding solar panel listed by Clyde Space for the 3u is only 29.2 watts.

3 kilos of Lithium Ion may be able to power the ion engine for as long as the battery lasts, but needs a cell to recharge the battery, and severly pinches the remaining mass for the cubesat.

Alternatively... if I recall my Heinlen, Phobos is said to have an orbital velocity reachable by a running human. The world record fastest runner, Usain Bolt, has demonstrated a peak speed of 12.42 meters per second, according to wikipedia. Taking this as a worst case orbital velocity, can we design a probe that can lithobreak with that kind of horizontal velocity? Worst case, a 45 degree impact into a mountian side against the heat shield.

Anyone want to refine the orbital velocity? or have any comments about either approach?

Edited July 22, 2014 by Rakaydos

[metaphor]

This sounds like an interesting idea.

Have you thought about using chemical propulsion rather than ion propulsion? Presumably it would be less expensive and the technology is mostly there already. The mission doesn't use too much delta-v so it might be beneficial.

From GTO it should take about 680 m/s to get to a lunar transfer orbit. From lunar transfer orbit to a Mars transfer orbit is about 500 m/s of delta-v. The lunar flyby can be used to change the orbital inclination to what is needed. Let's rule out aerocapture for now. Propulsive capture at Mars takes about 700 m/s, and then either aerobraking over multiple orbits or 750 m/s of propulsion to get into a Phobos transfer orbit. Circularizing at Phobos takes about 550 m/s. Circularizing could be done with Phobos gravity assists, but considering you would only get single-digit m/s change in speed with each pass, it might take a few hundred orbits (however, you could still get lots of pictures from the flybys). So that's a total of 1880 m/s assuming aerobraking and gravity assists. However, if using low-thrust ion propulsion, that delta-v increases to about 3000 m/s, depending on the thrust of the engine.

An ion engine with a specific impulse of 1800s would need a mass ratio of 1.2 to get the required delta-v. A hypergolic chemical engine with a specific impulse of 300s would need a mass ratio of 1.9, while an even simpler monopropellant engine with a specific impulse of 230s would need a mass ratio of 2.3.

Assuming a 4 kg spacecraft (is that the right number for a 3U cubesat?), an ion engine would need 0.7 kg of xenon, a hypergolic engine would need 1.9 kg of fuel, and a monopropellant engine would need 2.2 kg. The downside of the ion engine is that it's more expensive, low thrust, and not well tested, and has a high power requirement, so things like solar panels and other supporting equipment would take a more significant part of the spacecraft. So you would be left with a mass budget of about 2.5 kg for non-propulsion mass if using an ion engine, and about 1.5 kg for the chemical options. A chemical engine would also not have a problem landing on Phobos.

Another option for the carrier rocket: instead of piggybacking on a GTO launch, the cubesat could piggyback on an actual Mars launch. There's quite a few of those over the next 5 years.

[p331083]

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

Theres a whole host of mods that can fix that. Fact is youre not gonna get a super accurate sim type program on a modern desktop computer, let alone program as big and sandboxy as KSP.

[Rakaydos]

Did a bit of refinement in Wolfram Alpha for a Phobos Lithobreak. At an altitude of 13 km from mass center (so just a few hundred meters below phobos's highest mountian) orbital velocity is just under 7.5 m/s, and that will be barely a glancing hit.

If we can build the cube sat such that, say, the solar cells dont snap off when we bounce and sled, Lithobreakining seems a resonable alternative to a high IsP engine.

[christheman200]

I'd like to see you propose crashing into Phobos to the IAU.

[Rakaydos]

I'll just have to use words like "Low velocity Tangental lithobreaking," for the sledding approach, or "Mars-Phobos L1 controlled desent" for an approach that uses how small phobos's SoI is to minimize impact velocity.

[christheman200]

I think you guys might have had a chance of performing some real science in space if you had stopped changing your objectives and goals as you went along. Flying by Mars as a first space mission for any agency is absolutely ridiculous.

[Rakaydos]

I think you guys might have had a chance of performing some real science in space if you had stopped changing your objectives and goals as you went along. Flying by Mars as a first space mission for any agency is absolutely ridiculous.

Agreed, which is why we've hardened up on a 5 mission plan:

Mission 1: LEO plant lab/credibility mission

Mission 2: LEO Propulsion test

Mission 3: Solar orbit Mission w/ earth capture

Mission 4: Mars capture

Mission 5: Phobos

This topic is supposed to be for mission 4 and mission 5