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Could a modified Apollo spacecraft have been used to do a manned misson to Phobos?


szputnyik
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I've read that a manned flyby of Venus was planned. It would have used the Apollo spacecraft without the LM (only the LM engines would have been present) and taking along the spent S-IVB stage as a "wet workshop" so the crew could have spent the journey in a somewhat cramped space station-like environment instead of the even more cramped CM.

Could the Apollo spacecraft have been used for a similar mission to Phobos? Instead of the LM engine, they could have taken along a modified LM similar to the Soviet Lunniy Korabl with only the Apollo LM's ascent stage short-fueled and small landing struts, since Phobos' gravity is so small. A Mars aerocapture would have been used to put them into Mars orbit. The S-IVB stage would contain the propellant necessary to return to Earth. The journey there would've been pretty cramped in the CM, but on the homewards trip, the spent stage would become a wet workshop. After Earth aerocapture, they would have landed on the next orbit.

Do you think this mission would have been doable in the mid 1970s using the Apollo spacecraft?

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This is just based on some quick estimates in my head, so I may be entirely off base here, but I don't think S-V could have gotten a ship to a parking orbit near Venus and then back to Earth. If such a mission was planned, it sounds like it would use a fly by of Venus to alter trajectory for the return trip foregoing actual capture to Venus orbit. That means, you don't have to expend any fuel to return from Venus to Earth. Everything is done by Venus' gravity. Furthermore, you don't have to wait for a return window. Instead, you are flying a sub-optimal trajectory, but because you are fly-by boosted, you don't have to expend fuel on that either. Finally, the fact that Venus has a much shorter period than Earth, the entire mission would be under a year in duration.

Compare that to a Mars mission. The trip there is straight forward enough. It shouldn't take more fuel than a trip to Venus. Not by a significant margin, anyhow. And yes, you can aerobrake to capture. But then what? You are in parking orbit near Mars, and you have to get home. First, you have to wait for a window, and then you have to burn a lot of fuel to escape Mars and get to a transfer orbit. This is something Venus mission would not have to do, and it's something for which there isn't going to be enough fuel on anything S-V could lift. And even if you managed to somehow get enough fuel for that, maybe with an LEO rendezvous, you are now dealing with a 2+ year mission. Something that's much harder to prepare for, and you are suggesting that the first 7mo+ of that are spent in Apollo CM?

So yeah, I'd say, no, this was never a possibility for a S-V mission. LEO rendezvous mission to Mars could have been organized, but it would require 2+ S-V launches to get everything you need to LEO, and then move on from there.

P.S. You did give me a great idea, though. I'm going to repurpose either my Minmus lander or Mun Shot I for a Venus fly-by for a bunch of Science points in career mode. I have to go do some math now.

Edited by K^2
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Trans-mars insertion would be done by the S-V upper stage. It would be about an additional km/s of delta-v, so the total payload mass would need to be lower.

You'd use an Apollo13-style LM descent stage to perform the Mars orbital insertion burn; the stage would separate from the CSM after arrival at Mars. I'm too lazy to do the math right now, but its mass would probably be about the mass of the Apollo LM: It doesn't need to be inhabitable, nor does it need specifically high TWR, it's just a fuel tank and an engine, but on the other hand it needs to provide more impulse than the LM, as it also needs to decelerate the CSM.

Rendezvouz with, landing on and liftoff from Phobos would be done using the CSM RCS (Escape velocity is 11m/s, so expect a total rendezvouz/landing/liftoff/escape budget of ~50m/s).

The CSM would then perform trans-earth insertion.

The main problem would of course be the much higher CSM mass, to provide life support for over an year. So my overall guess is: No, it probably couldn't, but with todays tech (Life support, computers -> lower CSM mass; more reliable tech, more precise simulations -> Lower delta-v safety margins), it probably could.

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This is not ksp we do not get science points for recovering a pod that landed on Phobos. What are they going to do when they get there that makes it worth it, and how much does the equipment to do that weigh plus fuel to move that as well.

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Keep in mind that this would've happened during the Cold War, a few years after the last Apollo moon mission. It would've "worth it" because Americans managed to put a man on the moon of another planet and safely returned him, while the Soviets couldn't even put a man on our own moon.

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No way that was even remotely possible. The Apollo CSM generated electricity with fuel cells, which uses propellant. It was limited to a week or two of life support, that's about it. It would have to be a different spacecraft for longer trips.

Plus, the Saturn V might have had enough dV for an interplanetary flyby (but I doubt it), but with orbital insertion burn around Mars or Phobos, and a Mars departure burn at the end of the mission would be out of the question.

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Insertion, as OP noted, could be done with aerobraking. Then you only need enough fuel to circularize, and that's definitely manageable. It's the burn for the return trip that's completely out of the question with the S-V for your lifter.

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It was likely doable in the 70's. By the time NASA closed down the NERVA research in '72 they had an engine with 75,000lb of thrust and an ISP exceeding that of a kerbal NERVA. I've always understood that the whole reason they cancelled the NERVA itself was specifically to prevent the ensuing space-race to mars that unveiling tech like that would have caused. The US simply couldn't afford it.

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Are you joking? NERVA had an empty mass nearly that of the entire Apollo CSM. Fueled up it was more than 3x as heavy. Saturn V simply could not lift NERVA-based craft to LEO in one go. It would take multiple launches and an orbital assembly.

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I don't think the NERVA was as far as a long shot as you are saying if you consider when it would have been implemented. If funding had continued the Saturn 5 would have continued to be improved with F1-A engines on the table for an additional mega-newton of launch thrust each, and booster upgrades adding up to 8 additional F1 engines as strap on. Given this enhanced lift capability and the enhanced thrust and isp a NERVA engine would give the IVB stage I think it would make up for the slightly more than 3 times dry weight compared to the chemical IVB.

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The sort of modifications you'd need would amount in a complete redesign. Let's call our redesign Ares, just for tradition's sake.

You'd need more delta-V, a better power source, more space(and more crew, for psychological reasons)and better life support. Also radiation protection. You'll also need a higher gain antenna, both on the CSM and Mission control. And you need to lift it all to orbit, so more Saturn-V launches a mission at a minimum.

Let's tackle those in order.

Delta-V and Power: Bimodal NERVA engine, which is launched into low orbit with it's fuel tank(LH2, so pretty huge.) Heavy, but no personnel on this launch, so no "slowpoke launch" losses(Keeping Gees down means the rocket has to stay in atmos and without orbital speeds for longer, so more fuel burned.) Probably a Saturn-V launch, then. It'll be recovered and reused, because no one wants radioactive fallout due to reentry disposal.

We'll call this all the Service Module.

More space, life support and radiation protection: Ohhhhboy this is a hard one for 1960's tech. Kelvar won't be invented until the 70's, so either we wait or assemble it in orbit.

Probably wait. Designing the Service Module is going to take a bit.

Once Kevlar comes out, we can make an inflatable Crew Module. It'd look, when inflated, like a thick doughnut suspended to a corridor through the doughnut hole by other inflated corridor/cable(s). The corridor/cables allow access to the Central Corridor, which leads to the Reentry Module and the Lander on the 'bow', and Service Module at the 'stern'. The Central Corridor will probably have a folding antenna and observation equipment, as well as a secondary bridge and a machine room. We spin either the whole ship or the Central Corridor for gravity(+2 year mission, exercise is not enough.)

The Doughnut would have two decks: a lower, outer deck for hydroponics, waste processing and such, and a inner, higher deck for crew quarters and labs. The outer decks would probably be lined with lead, polyethylene and water storage(NOT touching) for some radiation protection.

The rest of radiation protection will probably take the form of ingestion of retinoids and iodine pills, which may not be all that recoverable.

Solar panels would line all but the inner face of the Doughnut, for additional/emergency power.

The Crew Module will also be recovered and reused.

The Reentry Module and Lander will be the last Module launched, as it will serve as the crew bus to the Ares. The Reentry Module will carry all 12(yes, twelve, both for psychological reasons and for all the fields required to explore a planet) back down to Earth at the end of the mission, as well as act as the main bridge for the whole vessel. So a larger Command Module.

The Lander would be substantially different, however(you didn't think we'd just go to Phobos, right?) It'd have to get down with three men to the Martian surface and back up, probably repeatedly and with no guarantee of onsite refuel.

So it'd probably land via parachute and airbags, albiet not disposable ones(they'd be deflated after each landing.) Then launch back into orbit on LH2 and O rockets.

Imagine a pyramid with rounded edges, with the cabin(a relatively small one) on top and engines on the bottom. Deflated airbags dot the bottom in such a manner as to completely cover and the engines it when inflated. 3 parachutes on top to slow down the lander prior to landing, which surround a docking node for when you get back up to Ares. RCS is provided by tiny LH2/O thrusters.

The most you'd need for a Phobos Lander is a variant of the Lunar Escape System with orbital computers. And even that is more for orbital maneuvers than actual landing/takeoff.

Mission Profile:

1. Launch of the Service and Crew Modules(deflated) into Low Earth Orbit a month in advance. The Modules are docked via remote control.

2. Launch of a crew shuttle(based off the Apollo Crew Module) and a equipment launch three weeks in advance. Carries only 3 men plus supplies and equipment, because they're going to inflate the Crew Module, connect pipes and wires, install what couldn't be carried up in the initial launch, etc. Basically final assembly.

3. Launch of the Reentry Module/Lander a week in advance. Carries the rest of the crew plus the rest of the equipment and personal effects. The week is spent finishing final assembly and activating the NTR.

4. Earth-Mars Window, Ares performs the injection burn to Mars(Final GO/NOGO. Beyond this, your arse is committed.)

5. 6 month long coast to Mars, on a strictly nonsmoking flight. You'll need a good head-shrink or two somewhere in the selection process. The Central Corridor's observation equipment could be used for astronomy.

6. Ares reaches Mars flyby orbit and performs a braking burn for capture.

7. A year of orbital/landing operations whilst SCIENCE is done. Samples are collected for further study.

8. Mars-Earth Window opens. Ares performs another transfer burn.

9. Another 6 month coast.

10. Ares brakes into Low Earth Orbit after 2 years of continuous operation.

12. Unless a cheaper method of crew transport is invented and used, the crew and the samples ride the Reentry Module to a water landing on Earth.

13. OH NOES

14. Ares is left in orbit for future reuse.

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No way that was even remotely possible. The Apollo CSM generated electricity with fuel cells, which uses propellant. It was limited to a week or two of life support, that's about it. It would have to be a different spacecraft for longer trips.

Plus, the Saturn V might have had enough dV for an interplanetary flyby (but I doubt it), but with orbital insertion burn around Mars or Phobos, and a Mars departure burn at the end of the mission would be out of the question.

Who says that they would do an insertion burn?

Mars has a significant atmosphere. A low flyby could probably aerobrake a ship into orbit.

Now clearly there are still issues, and even then, the rocket and capsule may require extensive modifications to squeeze enough Delta-V (about 4300 m/s after getting to LEO) and maneuverability out of it for a rendezvous/landing with either of Mars's moons.

Also, Phobos is scary, One hard step could send someone from Stickney crater to L1 and therefore Mars orbit.

Also, it is not entirely inconceivable that you could actually mess up Phobos's rotation with a hard impact, that is to say, tidally unlock it... I am not sure what the torque keeping it locked is, nor do I know the maximum torque that could be exerted to kill rotation is, but I'm guessing that it isn't much.

Finally, coming back could be troublesome, as it requires an additional 1400 m/s Delta-V.

As Fuel required scales very quickly with delta-V required, the rocket requiring only 200 m/s more Delta-V may well be enough to make the mission substantially more difficult, assuming that the payload weight is comparable.

For example, one calculation I did had a vehicle require 5.5% more fuel to move a tiny payload to 15 km/s than to 14.8 km/s, despite this only being a 1.3% increase in velocity and a 2.7% increase in kinetic energy.

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Actually, taking a second look at it, the Ares I designed could use some improvements:

1. Forget using the Reentry Module as a bridge; the secondary bridge is now the bridge, period. The Central Corridor, already having observation equipment(and hence, navigation) becomes the Conn.

2. The Service Module LH2 tank is also inflatable(The interior support needed to hold up the Crew Module remains solid, however), for space reasons.

3. The Reentry Module Launch comes with a assembly-needed Docking Pier, to support up to 8 or 12(Depends on design) crew shuttles, payload packages, Landers, and Reentry Modules radially.

4. The Service Module only launches with half the fuel rods, in shutdown mode, to minimize fallout in case of failure. The Equipment launch carries the other half.

5. Between burns, the vessel is pointed perpendicular to the sun and spun up using RCS. This allows even heating of the entire spacecraft and gravity at the same time.

6. RCS uses LH2/O thrusters, as we're already carrying both for the lander.

7. Speaking of O2, the Docking Pier is also extra O2 and possibly LH2 storage.

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No on Phobos but yes on Mars.

Originally they were going to build the Nova rocket.

Then the Saturn-V with strap on SRBs.

After that the Saturn-V with a Nerva uppers.

But then they built the shuttle... and now we know not to build shuttles anymore.

The dream was real though.

zmars69a.jpg

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Aerobraking around Mars would be tricky. Its atmosphere is very thin. To drop to orbit from interplanetary speeds would probably require dipping down below the tops of the mountains. You'd have to add weight for a second heat shield (one for aerobrake around Mars, and another for Earth return.)

Stephen Baxter's novel Voyage lays out a pretty plausible chain of events in an alternate history where NASA went to Mars in the late 80's rather than build the shuttle and do robotic interplanetary science. In that novel, they use several launches to lift and assemble a "propulsion stack" consisting of transfer engines and external fuel tanks. Then the astronauts and mission stack, which includes a wet workshop for habitation, are launched and docked to the propulsion stack. The launches use an upgraded Saturn V with solid boosters to increase the payload capability. The mission relies on a Venus slingshot to reach Mars.

Someone made a pretty good video of Baxter's proposed mission using Orbiter:

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Current Mars probes use high altitude aerobraking without a heatshield, but they do multiple passes over several months. That isn't very practical for a manned mission. More time in space means more radiation mitigation (heavier shielding) and more supplies.

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Ok since your basing this on the Apollo Venus Flyby project, lets take that mission apart and analyse it.

Mission consists of Saturn V, Apollo CM & SM and the LM is replaced with an airlock and supplies.

Saturn V 1st and 2nd stages are used to lift the payload to orbit, S-IVB is used to burn into a Venus free return transfer, any remaining fuel is vented into space.

S-IVB is then converted to a habitat for the long duration flight, mission swings by Venus and returns to earth, S-IVB is ejected and Apollo SM engine is used for Earth capture.

So now lets turn that to mars. Since we're wanting to land rather than fly by, we don't need the precise timing of a free return transfer, so that's good, but also means we'll have to save fuel for a return transfer.

This is our problem, Either we do not vent the fuel, from the S-IVB on the way to mars, and thus the astronauts do not have a habitat for the outbound trip, or you do and have to jettison it and use the Apollo SM engine for the return burn. Unfortuinately you now don't have the Habitat for the return trip, and still don't have the delta-v (only 2,800m/s on the Apollo) to return to earth. Another problem is since you want to land, you've got to bring a lander, now you can't bring the airlock and supplies that would have taken it's place.

So the only way you could do it would be to skip the wet workshop plan, and simple use the S-IVB for outbound and return, (but my research is suggesting even the S-IVB didn't have the delta-v for that) but then you have to leave the astronauts in the crapmt Apollo for over a year.

I do want to point out, I'm not saying it couldn't be done with early 1970's tech, I'm saying that it couldn't be done with a modification of the Apollo.

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Current Mars probes use high altitude aerobraking without a heatshield, but they do multiple passes over several months. That isn't very practical for a manned mission. More time in space means more radiation mitigation (heavier shielding) and more supplies.

The Mariner, Mars (USSR), and Viking missions did not, as far as I can tell, use aerobraking to change their orbits. Mars Odyssey and the MRO did, but they still had to do an insertion engine burn before aerobraking. MRO, for instance, had to do a 27 minute, 1000 m/s burn to get captured, before circularizing by aerobraking, and it took 445 orbits over 5 months to circularize. Mars Odyssey had to do a 1400 m/s burn for MOI, then do 380 orbits over 3 months for circularization.

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Are you joking? NERVA had an empty mass nearly that of the entire Apollo CSM. Fueled up it was more than 3x as heavy. Saturn V simply could not lift NERVA-based craft to LEO in one go. It would take multiple launches and an orbital assembly.

Of course you'd have to make modifications to the setup as a whole - the question "could a modified Apollo spacecraft have been used for a manned mission to Phobos" implies some deviation from the original configuration. We are after all not talking about a simple jaunt to our own moon.

The mods are likely fewer than you'd think though. One of the uses slated for the NERVA was was part of the Saturn-launcher-based RIFT programme - NERVA upper stages placed in LEO to act as tugboats for moving things to higher orbits, or used to lift 170-odd tonnes at a time to LEO. The proposed vehicle was a Saturn S-IC first stage, S-II second stage, S-N (Saturn, Nuclear) final stage. That's two stages of off-the-shelf technology and a bit more work on one near completion. Even Von Braun had them lined up to be the engine that'd take humanity to Mars. Apollo based craft? Maybe not (if only because you don't lock people in a container that small for an interplanetary flight). But sharing the Saturn-based launch vehicle and using other NASA tech that was tested and available in the '70s? Certainly.

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That's the difficult part. Maybe the astronaut would have raised edible insects in a container and instead of space food, they would've packed insect food.

Or even better they could have raised edible bacteria because bacteria are even teenier and they eat even less right? Alternatively we can choose to not break the second law of thermodynamics.

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That's the difficult part. Maybe the astronaut would have raised edible insects in a container and instead of space food, they would've packed insect food.

Or even better they could have raised edible bacteria because bacteria are even teenier and they eat even less right? Alternatively we can choose to not break the second law of thermodynamics.

They could raise edible plants, which don't even need to eat.

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