Mars mission with current rockets.

[Nuke]

i dont think rocketry is the limit for a mars mission. life support, refueling, making oxygen/water/food, radiation, electrical power, human endurance, regulatory bs, funds, those are the limits. 

Edited December 6, 2021 by Nuke

[kerbiloid]

45 minutes ago, Nuke said:

i dont think rocketry is the limit for a mars mission. life support, refueling, making oxygen/water/food, radiation, electrical power, human endurance, regulatory bs, funds, those are the limits. 

The latter are limits because the former is too uncapable and requires tens of launches making the whole enterprise highly unreliable.

[razark]

The main constraint is money.  Get enough of that, and you can do almost anything.

[sevenperforce]

Block 1B is supposed to be able to throw 42 tonnes to TLI. What can it throw to Mars? And what is our best estimate of what kind of propellant residuals EUS would have if launched empty to LEO?

[tater]

3 hours ago, sevenperforce said:

Block 1B is supposed to be able to throw 42 tonnes to TLI. What can it throw to Mars? And what is our best estimate of what kind of propellant residuals EUS would have if launched empty to LEO?

To use EUS as a TMI stage? Interesting.

[sevenperforce]

1 hour ago, tater said:

To use EUS as a TMI stage? Interesting.

If the question is "how do we send stuff to Mars without Starship?" then that might actually be a viable use case for SLS...not as a launcher, but as a way of throwing heavy stuff to Mars. It doesn't have the cadence to support orbital assembly but it might be able to finish everything out at the end.

The new RL-10C-3s for the EUS are supposed to get 460.1 seconds of specific impulse. 

This familiar image outlines some of the capabilities that the EUS is supposed to have in comparison to Block 1:

And here is this (which seems like a good an estimate as any for EUS):

 

Trans-lunar injection is 3.2 kilometers per second. If EUS on SLS Block 1B Cargo can push 42 tonnes (plus its own 13.13-tonne dry weight) to TLI, then it would need to leave LEO with an m₀ of 112.1 tonnes. Given that it would mass 155.4 tonnes at staging, this means it stages just 1,474 m/s shy of LEO.

Now, the SLS core would stage at a higher velocity if it wasn't pushing a 42-tonne payload on top of the EUS. The SLS has a dry mass of 85.3 tonnes and a prop mass of 987.5 tonnes, for a total wet mass of 1,072.8 tonnes. Add the EUS and a 42-tonne payload, and that's a launch mass of 1,228.2 tonnes and a burnout mass of 240.7 tonnes. With the 452 second vacuum specific impulse of the RS-25s, that's a total of 7,224 m/s. We can use this since gravity drag, aerodynamic drag, and pressure drag will be roughly the same. Yes, I'm ignoring the boosters; they don't make much of a difference in this scenario. If you take off the 42 tonnes, then your launch mass becomes 1,186.2 tonnes and your burnout mass becomes 198.7 tonnes, for a total of 7,920 m/s.

So a naked EUS would stage around 696 m/s faster than an EUS carrying a 42-tonne TLI payload, meaning it would only need to burn 778 m/s to reach LEO. It would have some sort of docking/berthing adapter, of course, but let's not worry about that just yet. It would only need to burn 18 tonnes of propellant to reach LEO, leaving it with 82.3 tonnes of residuals.

Now we turn to our Mars payload, assembled in LEO using some combination of commercial launch vehicles. How big could it be? Well, at 460.1 seconds of specific impulse, a stack needs to burn 65% of its total weight to get the 3.6 km/s of dV required for a Hohmann transfer to Mars. 82.3 tonnes divided by 65% gives you a total stack weight of 126.6 tonnes and a burnout mass of 44.3 tonnes. Once we subtract the dry mass of the EUS, that's about 31 tonnes injected to Mars. Assuming you have to brake in with storables, that should give you about 23 tonnes to a high, eccentric Martian orbit (a la the "podsadka" approach referenced upthread) or 15 tonnes to low Martian orbit, before subtracting the dry mass of the propulsion unit.

What does that give us? Well, not much. For a best-case scenario with the eccentric Martian orbit, that's probably around 21 tonnes of useful payload.

Architecture would need to look something like this:

• Pre-positioned hab, 16.8 tonnes launch mass. Launched direct to TMI by FHe, performs direct EDL at Mars.
• Descent/ascent vehicle, 31 tonnes launch mass. Launched to LEO by FH(ce), then sent to TMI by EUS, then burns its own engines to enter eccentric Martian orbit.
• Return propulsion module, 16 tonnes launch mass. Launched direct to TMI by FHe, uses about 5 tonnes of its propellant to enter eccentric Martian orbit.
• Transfer hab and Martian orbital propulsion module, 18 tonnes launch mass. Launched to LEO by FH.
• Beefed-up Crew Dragon, 13 tonnes launch mass. Launched to LEO by Falcon 9, docks with the transfer hab, and then the whole stack is sent to TMI by EUS.

The transfer hab would be spartan -- only about 8 tonnes. The orbital propulsion module attached to the transfer hab would brake it and Crew Dragon into eccentric Martian orbit, where the vehicle would rendezvous with the waiting descent/ascent vehicle and the return propulsion module. Checkouts would ensure that both were fully operational; if the return propulsion module showed issues necessitating an abort, the descent/ascent vehicle would have ample dV to perform the TEI burn. Crew would enter the descent/ascent element, reach the surface and the hab, have their Martian stay, and then return to the waiting transfer hab, Crew Dragon, and return propulsion module. Then the return propulsion module would burn for TEI with Crew Dragon and the transfer hab.

Required launches:

• 2X Falcon Heavy Expendable
• 1X Falcon Heavy (core expended)
• 1X Falcon Heavy
• 1X Falcon 9
• 2X SLS Block 1B

The two SLS launches would be two years apart, which solves the cadence problem. 

I believe all these mass budgets are roughly in line with what @RCgothic proposed upthread. The difference is that I'm using Falcon Heavy's expendable configuration where necessary and I'm using an eccentric Martian orbit rather than a low Martian orbit. I can use eccentric Martian orbit because using EUS for TMI allows for a very large monolithic descent/ascent element with the necessary dV to make up for needing to go past LMO. I'm also splitting the propellant budget up so that the crew vehicle doesn't have to brake all its return propellant into Martian orbit when it arrives.

Edited December 7, 2021 by sevenperforce

[tater]

The only problem would be Crew Dragon duration. Not sure what limits the on-orbit stay of Dragon right now.

[sevenperforce]

23 minutes ago, tater said:

The only problem would be Crew Dragon duration. Not sure what limits the on-orbit stay of Dragon right now.

It can take 210 days docked to the ISS before the radiation environment starts to degrade the electronics, particularly the solar arrays. A beefed-up Crew Dragon for the Martian return would presumably also have beefed-up radiation protection and rad-hardened electronics. Costly but not a lot of mass growth.

[RCgothic]

35 minutes ago, sevenperforce said:

It can take 210 days docked to the ISS before the radiation environment starts to degrade the electronics, particularly the solar arrays. A beefed-up Crew Dragon for the Martian return would presumably also have beefed-up radiation protection and rad-hardened electronics. Costly but not a lot of mass growth.

Also note that a Mars Dragon would be doing very little independent flight. It could probably undock and re-enter on battery power alone.

[tater]

What about RCS? Is the duration entirely limited by radiation concerns, or are there any issues with the hypergolics for more than XXX days?

They could be addressed, certainly, but it's a factor to consider.

[sevenperforce]

1 hour ago, RCgothic said:

Also note that a Mars Dragon would be doing very little independent flight. It could probably undock and re-enter on battery power alone.

Yeah, the Dragon would really only be doing a handful of actual things:

1. Fly independently from the Falcon 9 launch vehicle to rendezvous with the transfer hab; dock (exactly what it does with the ISS right now)
2. Assist the transfer hab in holding position while the EUS mates to it
3. Stay attached to the transfer hab during coast
4. After Martian orbital insertion, assist the transfer hab in holding position while the return propulsion unit mates to it
5. Assist the transfer hab in holding position while the descent/ascent element docks to it
6. Stay attached to the transfer hab during the Martian surface mission
7. After the Martian surface mission, assist the transfer hab in holding position while the descent/ascent element docks to it
8. Stay attached to the transfer hab during coast
9. Undock shortly before Earth entry interface, adjust course, and re-enter.

Only a single docking-undocking sequence. No free flight.

Of course, that's for an eyeballs-out burn. For a more pleasant eyeballs-in burn, the Dragon would need to carry the EUS mating adapter in its trunk. But I don't know whether the docking port on the nose of the Dragon is up for pushing an 18-tonne payload through TMI.

1 hour ago, tater said:

What about RCS? Is the duration entirely limited by radiation concerns, or are there any issues with the hypergolics for more than XXX days?

They could be addressed, certainly, but it's a factor to consider.

The Red Dragon proposal would have landed on Mars using SuperDracos and I don't think there was any particular concern about how long the hypergolics would last. I suppose they call them storables for a reason.  

[tater]

1 hour ago, sevenperforce said:

The Red Dragon proposal would have landed on Mars using SuperDracos and I don't think there was any particular concern about how long the hypergolics would last. I suppose they call them storables for a reason.  

Yeah, unsure what it is rated for WRT crew is all, and mission duration would become years. I'm sure they could work that issue, but it's not "off the shelf" they'd have to get the duration officially extended.

[sevenperforce]

Falcon Heavy is fairly limited by its 5-meter fairing. What kind of a Martian surface hab can you realistically fit in that kind of cross-section?

[kerbiloid]

A Harmony-sized water cistern with a room inside, with a foldable bed and several blankets.

The water is for both drinking and rad protection. 
The bed is to let/make him sleep all way long and not think about what happens around.

[sevenperforce]

10 minutes ago, kerbiloid said:

A Harmony-sized water cistern with a room inside, with a foldable bed and several blankets.

The water is for both drinking and rad protection. 
The bed is to let/make him sleep all way long and not think about what happens around.

With the fairing stretch that Falcon Heavy is getting, it could loft both Harmony and Tranquility stacked end to end at the same time.

I'm more curious about how deployment would work.

[kerbiloid]

10 minutes ago, sevenperforce said:

With the fairing stretch that Falcon Heavy is getting, it could loft both Harmony and Tranquility stacked end to end at the same time.

I'm more curious about how deployment would work.

They are 7 m long each, 14 in total.

So, with diameter 4+ m and length just three meters longer than Salyut, the best way to deploy them is weld them together.

[sevenperforce]

4 minutes ago, kerbiloid said:

They are 7 m long each, 14 in total.

So, with diameter 4+ m and length just three meters longer than Salyut, the best way to deploy them is weld them together.

Yes, if you were launching a Harmony sized module and a Tranquility sized module at the same time, you could weld them together and put them on Falcon Heavy.

The important question, though, is how we would go about stuffing a Martian surface hab into a 5-meter diameter.

[tater]

is it landing vertically, or can it be biconic and land on the side? Then it is a stretched fairing, 5.4m, landing sideways—no need regardless to fit it IN the fairing, the fairing IS the hab.

Actually, I doodled such a thing a few years ago...

 

My doodle assumed vertical landing, and that was before we knew FH would also get a stretched fairing (which it is getting).

Old cargo Dragon to scale.

[sevenperforce]

23 minutes ago, tater said:

is it landing vertically, or can it be biconic and land on the side? Then it is a stretched fairing, 5.4m, landing sideways—no need regardless to fit it IN the fairing, the fairing IS the hab.

Actually, I doodled such a thing a few years ago...

My doodle assumed vertical landing, and that was before we knew FH would also get a stretched fairing (which it is getting).

Old cargo Dragon to scale.

Oh, interesting. That is a cool concept.

What's the limit of a skycrane landing?

If it landed vertically, then presumably you'd have some sort of doors so you could drive a pressurized rover right out and onto the regolith. If horizontal, then you would drive the rover out the back end.

For my more conventional approach, I was thinking of a two-stage skycrane. Put the hab and inflatable side modules behind an inflatable heat shield, and put a pressurized rover on top. The skycrane lowers the whole affair down to the ground, then severs the connection between the rover and the hab and lowers THAT to the ground next to it, then flies away.

[tater]

How much dv is needed to actually land? Use the vertical fairing, the nose has chutes to do much of the work. Underneath is engines, LES style for Crew Dragon (cosine loss), but designed not for LES, but soft landing on Mars.

Legs flip down per my image (maybe connecting as a ramp on one side), and with engines up at the nose, it lands VERY low to ground (self leveling). Rover can roll out, which gives to a 5.4m circle of which a rectangle is rover. One side can have an airlock, with stairs leading up to crew decks. You could probably get chutes, landing props, a rover deck, and 2 crew decks (stretched fairing height). Any excess volume for consumables.

That's 44 m² of crew floor area, kinda dinky. The question is, how light could those be, they are mostly open volume after all. What's FHce mass to TMI? F9e is ~8t to TMI, FHe is 16t. Just throwing away the core has to be in between.  They could send a few habs, only 1 needs the rover deck, the other can be 3 crew decks (66 m²) Maybe there could be an inflatable passageway to connect them (if the rover is capable of moving one)?

[sevenperforce]

39 minutes ago, tater said:

How much dv is needed to actually land? Use the vertical fairing, the nose has chutes to do much of the work. Underneath is engines, LES style for Crew Dragon (cosine loss), but designed not for LES, but soft landing on Mars.

I don’t imagine you’d need more than 400 m/s for landing. Perseverance popped its chute at 420 m/s airspeed, and so a couple of drogues should do plenty to get the descent speed down to something manageable. Of course, you need to reserve RCS props for the descent.

Having a single descent/ascent element has an abort mode advantage, because if you have a landing problem you can simply fire your ascent stage and return to orbit. But if you’re willing to accept a separate ascent and descent element, there are definitely some advantages. You can use solar power to crack LOX out of the Martian atmosphere and eliminate more than half of your landed mass.

And perhaps even more interesting: you can make your descent element do double duty. Most Martian landing architectures call for a pressurized rover that can dock to your hab. If you’re going to have a pressurized rover, then why not land your crew IN the rover? The lander module docks with your orbiter and the crew crawls through to the rover. The landing progresses much like Curiosity or Perseverance, albeit with a much bigger rover. Then the crew simply drives the rover over to a docking with the hab.

[SunlitZelkova]

Apologies if it is obvious and I missed it, but is the mission you proposed/created a conjunction class mission or an opposition class mission? @sevenperforce

Edited December 8, 2021 by SunlitZelkova

[sevenperforce]

2 minutes ago, SunlitZelkova said:

Apologies if it is obvious and I missed it, but is the mission you proposed a conjunction class mission or an opposition class mission? @sevenperforce

It can be adapted to either, but the phasing issues will probably be solved more readily with a conjunction class mission, if the surface hab can support that long of a stay.

If you want a larger surface hab, you can do orbital assembly with an inflatable heat shield and use either an expendable, naked Falcon Heavy or an EUS for TMI.

[kerbiloid]

https://www-energia-ru.translate.goog/energia/mars/condition.html?_x_tr_sl=auto&_x_tr_tl=en&_x_tr_hl=ru

[sevenperforce]

23 hours ago, tater said:

Legs flip down per my image (maybe connecting as a ramp on one side), and with engines up at the nose, it lands VERY low to ground (self leveling). Rover can roll out, which gives to a 5.4m circle of which a rectangle is rover. One side can have an airlock, with stairs leading up to crew decks. You could probably get chutes, landing props, a rover deck, and 2 crew decks (stretched fairing height). Any excess volume for consumables.

Another option I think I like better: use one half of the fairing as the heat shield and the other half of the fairing as the backshell. Adding PICA-X to one of the fairing halves couldn’t be too difficult, and you keep the existing separation mechanism (although you would need to have a modified PAF that separates from the Falcon upper stage). The fairing halves already have cold gas thrusters for orientation after separation; they would just need to be mounted with nozzles pointing through the backshell half of the fairing for orientation control during re-entry. Weight distribution would easily make it passively stable with lift, and the yaw thrusters would merely control the lift vector. The backshell half would also need an external supersonic chute a la Perseverance, and it could include fixed solar panels as well for power during coast. No matter if they burn off during entry.

The hab is oriented sideways in the fairing with the base oriented toward the heat shield side, so as it descends through re-entry it remains base-side-down. Once through the seven minutes of hell, the drogue on the backshell half pops. Once it fully inflates, the heatshield half is jettisoned, exposing the base of the hab. A skycrane is inside the backshell half, which separates from the hab before the skycrane lowers it to the surface.

This allows a central hab core room that’s up to 4 meters high and 4 meters wide, connected to two modules that can each contain expandable modules, with room for a logistics module on one end and a rover on the other. Low to the ground, maximum footprint.