Mars in three years

[Nibb31]

On 4/26/2017 at 3:38 AM, p1t1o said:

Its probably almost as impossible, but how would things change if the mission remit was manned, but without landing the astronauts on the martian surface?

That's pretty much what NASA's current 2030 plan is. 

 

I was all set with "yeah, we can do it!" Not in three years but but 2024. 

Then I scoped out three years of consumables fur a crew of six and then ballparked a spaceship (lander not inc) of 225t not inc tanks. With a non-hydrogen (because boil-off) propulsion system, probably raptor based, I come up with something like 3000t of fuel and 150t of tanks just you GET to Mars, nevermind land and return!

That's something like 60 falcon heavy launches just to get the fuel up there! It was at that point that I changed my tune. We need a better way to unite vehicle and fuel. Or an aeroshell to brake at both ends. But an aeroshell that big would be getting into ITS territory.

 

On 4/26/2017 at 11:56 AM, sevenperforce said:

How are you figuring consumables? Can you post your numbers? Trying to figure out what it would look like for a crew of 4. What kind of living space were you proposing?

From NASA's web site:

"A trip to Mars and back, for instance, may take more than three years and require the provision of thousands of kilograms of food. A crew of four on a three-year martian mission eating only three meals each day would need to carry more than 24,000 pounds (10,886 kilograms) of food."

That's 2.5 tons of food per astronaut. I remember reading somewhere that the total amount of consumables is close to 10 metric-tons per astronaut (which includes water, air, food, clothes, meds, and various other supplies). 

For habitable volume, there are studies like this one:
https://www.researchgate.net/publication/224407917_Activity-based_habitable_volume_estimating_for_human_spaceflight_vehicles

 

On 4/26/2017 at 11:56 AM, sevenperforce said:

How are you figuring consumables? Can you post your numbers? Trying to figure out what it would look like for a crew of 4. What kind of living space were you proposing?

Two part-pressurised service modules @60t each (each mostly 50t consumables) each end of a 20t hab. Hab is largest volume SLS can loft in a oner, 8m diameter. Two Orions docked radially. 70t propulsion module with radially attached tanks.  Comes to 230t.

For consumables, I used at least one of Nibb31's sources. A good one is at: https://intra.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/200440012725.pdf apologies if I screwed up the link as I had to type it manually.

Same value for food, 15t. Oxygen is related to calorific value, so is about  20t. Water for drinking, rehydrating food and food preparation comes to about 5.5 times food~82t! Though I allowed a little bit of reclamation. Water for hygeine I didn't even touch, and can apparently be ten times more than water for food/consumption. I also didn't account for atmosphere leakage, which could have been a nasty error.

Basically, the ship is going to have to be able to reclaim water and oxygen and turn carbon dioxide and electrical power into calories or half the habitable mass is going to have to be supplies.

 

Edit: The two service modules were for Apollo 13 style redundancy. Half power and rations is better than none. Other failures in the mission architecture I was considering have survivable abort modes. Mars insertion fails - free return. Earth injection fails - propulsion module exchange with tanker. Hab slow failure - Orion lifeboat. Earth insertion fails - direct return in an Orion. Catastrophic service module failure was one of the not-recoverables, so I went with two. Nasa would probably do it differently!

 

2 hours ago, RCgothic said:

Two part-pressurised service modules @60t each (each mostly 50t consumables) each end of a 20t hab. Hab is largest volume SLS can loft in a oner, 8m diameter. Two Orions docked radially. 70t propulsion module with radially attached tanks.  Comes to 230t.

For consumables, I used at least one of Nibb31's sources. A good one is at: https://intra.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/200440012725.pdf apologies if I screwed up the link as I had to type it manually.

Same value for food, 15t. Oxygen is related to calorific value, so is about  20t. Water for drinking, rehydrating food and food preparation comes to about 5.5 times food~82t! Though I allowed a little bit of reclamation. Water for hygeine I didn't even touch, and can apparently be ten times more than water for food/consumption. I also didn't account for atmosphere leakage, which could have been a nasty error.

Basically, the ship is going to have to be able to reclaim water and oxygen and turn carbon dioxide and electrical power into calories or half the habitable mass is going to have to be supplies.

Edit: The two service modules were for Apollo 13 style redundancy. Half power and rations is better than none. Other failures in the mission architecture I was considering have survivable abort modes. Mars insertion fails - free return. Earth injection fails - propulsion module exchange with tanker. Hab slow failure - Orion lifeboat. Earth insertion fails - direct return in an Orion. Catastrophic service module failure was one of the not-recoverables, so I went with two. Nasa would probably do it differently!

What do you mean by "Earth insertion fails - direct return in an Orion"?

 

I mean engine failure between Mars and Earth. The idea is to save the spaceship with an insertion burn but if that isn't possible the crew can ride in hot in one/two of the Orion capsules and the spaceship will burn up in earth's atmosphere. 

 

Free returns are somewhat limited for Mars, the total trip times vary between ~2.7 years, and closer to 5 years. Those windows clearly limit launch opportunities. While it's a good idea from a safety POV, human flyby missions for their own sake strike me as pretty silly.

 

The time frames also constrain LS requirements. You'd have a nominal, orbital mission trip time, and if the free return is shorter, you're good to go. If that timing doesn't work, then you might need substantially more expendables aboard for that contingency. I doubt NASA would plan on harmful food ratio levels as a possible abort condition, when that might mean doing so for really long periods of time.

 

 

https://trajbrowser.arc.nasa.gov/traj_browser.php?NEAs=on&NECs=on&chk_maxMag=on&maxMag=25&chk_maxOCC=on&maxOCC=4&chk_target_list=on&target_list=Mars&mission_class=roundtrip&mission_type=flyby&LD1=2018&LD2=2040&maxDT=8&DTunit=yrs&maxDV=10&min=DV&wdw_width=-1&submit=Search#a_load_results

 

 

You wouldn't want to go before 2024, there are some short total duration mission opportunities then:

https://trajbrowser.arc.nasa.gov/traj_browser.php?NEAs=on&NECs=on&chk_maxMag=on&maxMag=25&chk_maxOCC=on&maxOCC=4&chk_target_list=on&target_list=Mars&mission_class=roundtrip&mission_type=rendezvous&LD1=2018&LD2=2040&maxDT=8&DTunit=yrs&maxDV=10&min=DV&wdw_width=-1&submit=Search#a_load_results

~2.6 years, total.

2020/2022 are  >5 years total at best. So even the 8 year plan doesn't work. Dangit, physics!

 

On 4/26/2017 at 5:55 AM, RCgothic said:

I was all set with "yeah, we can do it!" Not in three years but but 2024. 

Then I scoped out three years of consumables fur a crew of six and then ballparked a spaceship (lander not inc) of 225t not inc tanks. With a non-hydrogen (because boil-off) propulsion system, probably raptor based, I come up with something like 3000t of fuel and 150t of tanks just you GET to Mars, nevermind land and return!

That's something like 60 falcon heavy launches just to get the fuel up there! It was at that point that I changed my tune. We need a better way to unite vehicle and fuel. Or an aeroshell to brake at both ends. But an aeroshell that big would be getting into ITS territory.

How are you figuring consumables? Can you post your numbers? Trying to figure out what it would look like for a crew of 4. What kind of living space were you proposing?

 

1 hour ago, RCgothic said:

I mean engine failure between Mars and Earth. The idea is to save the spaceship with an insertion burn but if that isn't possible the crew can ride in hot in one/two of the Orion capsules and the spaceship will burn up in earth's atmosphere. 

Ah, I see. Makes sense.

My preferred architecture for a manned Mars mission is to use two transfer vehicles which are each capable of aerobraking or aerocapture, plus two tankers that execute free-return and do a hot EDL at Earth. This really, really reduces the required dV and gives you a lot of extra redundancy/safety margin, along with reuse of all components. You can bring along unshielded modules for the outgoing journey but not for the homeward journey, if you're willing to dump them at Mars.

Two fully-fueled tankers plus two fully-fueled transfer vehicles (each with an onboard hab, supplies, and half the total crew) depart LEO on a free-return TMI. Once the TMI burn has been completed, each tanker executes a rendezvous with one of the transfer vehicles and pumps its propellant over. The tankers maintain their free-return trajectory; the two transfer vehicles adjust their trajectory from free-return to aerocapture. They then dock with each other. Rotating for simulated gravity is possible if desired, as their structure can handle the tensile load easily.

Upon arrival at Mars, the transfer vehicles separate, aerocapture and circularize in Mars orbit, then rendezvous again. One vehicle, the lander, transfers most of its fuel to the other one before separating and executing EDL. Once the mission is complete, the lander returns to orbit on its remaining fuel, does a rendezvous with the still-orbiting vehicle, transfers necessary propellant, and the two return to Earth together.

[tater]

What is going on?

 

https://trajbrowser.arc.nasa.gov/traj_browser.php?NEAs=on&NECs=on&chk_maxMag=on&maxMag=25&chk_maxOCC=on&maxOCC=4&chk_target_list=on&target_list=Mars&mission_class=roundtrip&mission_type=rendezvous&LD1=2018&LD2=2040&maxDT=8&DTunit=yrs&maxDV=10&min=DV&wdw_width=-1&submit=Search#a_load_results

I had made a post about possible launch dates showing that round trip times (including surface or orbital time until a return window) are only desirable 2024 and on. Some of the pre-2024 windows mean 2X the total trip time.

 

Looks like the server is going haywire.

[tater]

No kidding, this thread lost 30+ hours of posts.

[sevenperforce]

23 minutes ago, tater said:

No kidding, this thread lost 30+ hours of posts.

I'm seeing Nibb as the author of maybe a dozen posts, including some of mine, all merged into one.

 

I made a thread to report the issue, and the thread disappeared, lol.

On topic, SLS delayed until at least early 2019:

https://arstechnica.com/science/2017/04/senior-official-nasa-will-delay-first-flight-of-new-sls-rocket-until-2019/

Oh, I see what you mean! My replies are actually here, but merged into Nibb's post.

[Nibb31]

Lol! It looks like I'm assimilating all the posts in the thread. Resistance is futile! 

[tater]

I wonder what the maximum direct entry speed could be for an Earth reentry, anyone know? 

[YNM]

Too long time -> lots of consumables. (edit) And breathing space.

Shorter time -> more fuel.

I know this might sounds crazy, but how far can we tradeoff from each other there ? I mean, if you carry lots of fuel it can't really spoil (and faster mission benefits from less loss as well), so what do you think ? Is anyone willing to really, really run the numbers ?

Edited April 28, 2017 by YNM

[tater]

A mission is possible in ~1.25 years (30 day stay on surface) total duration, but the Earth entry is on the order of 20km/s, with a total dv from LEO on the order of 9 km/s. More fuel decreases required supplies, but of course a higher velocity transfer kills the free returns.

[sevenperforce]

10 hours ago, tater said:

I wonder what the maximum direct entry speed could be for an Earth reentry, anyone know? 

SpaceX lists the Earth re-entry as 12.5 km/s or a bit more, but with peak acceleration at 3 gees. Mars entry is lower, at 8.5 km/s, but you end up with up to 6 gees due to the thinner atmosphere.

9 hours ago, YNM said:

Too long time -> lots of consumables.

Shorter time -> more fuel.

I know this might sounds crazy, but how far can we tradeoff from each other there ? I mean, if you carry lots of fuel it can't really spoil (and faster mission benefits from less loss as well), so what do you think ? Is anyone willing to really, really run the numbers ?

The ITS presentation had a lot of these numbers provided -- delta v vs payload. So you can start there. One of the issues is mission duration.

[YNM]

9 hours ago, tater said:

A mission is possible in ~1.25 years (30 day stay on surface) total duration, but the Earth entry is on the order of 20km/s, with a total dv from LEO on the order of 9 km/s. More fuel decreases required supplies, but of course a higher velocity transfer kills the free returns.

Would "more ablatives" work ? If it does, lets put that back in consumables and can anyone run the numbers there ?

3 minutes ago, sevenperforce said:

The ITS presentation had a lot of these numbers provided -- delta v vs payload. So you can start there. One of the issues is mission duration.

Noted, when I have the time I'll look around.

[tater]

OK, I reran the same thing I did yesterday, and I am not seeing the ~1.25 missions at all. Very odd. All I did was up the max dv from 10 to 11, and I got much better duration, with much higher reentry velocities back at Earth. Not working. They had 30 day stay times, now the least I see is 112.

Edited April 28, 2017 by tater

[sevenperforce]

9 hours ago, tater said:

A mission is possible in ~1.25 years (30 day stay on surface) total duration, but the Earth entry is on the order of 20km/s, with a total dv from LEO on the order of 9 km/s. More fuel decreases required supplies, but of course a higher velocity transfer kills the free returns.

Wait, how are you getting 9 km/s? I'm getting 10.2-10.6 minimum for the round-trip, assuming aerobraking direct from a minimum-dV Hohmann transfer at both ends. 

If fully-refueled in LEO, my mini-ITS can deliver 69 tonnes to Mars orbit via aerocapture and 47 tonnes to the Martian surface with propulsive landing. One mission profile I like is to put fuel in Martian orbit, either by sending a tanker along or by sending an ISRU-equipped lander ahead to land on Mars, make the fuel, and return to Martian orbit. That should be able to permit speedy transfers both ways.

[tater]

I was just checking what I ran on the nasa page, and I am getting wildly different results than yesterday. I even upped total dv to 20... still the best is 2.5 years.

Really bizarre. I had round trip checked for sure because I had a reentry speed. Changing the total allowed dv doesn't actually change the range of mission cvs, either. Right now I am seeing totals around 5, even if I set it to 20.

Edited April 28, 2017 by tater

[tater]

OK, I figured out what I did. Set max duration to 2 years.

You can do a round trip Mars mission in the right years in under 400 days in 2018, 2033 with an Earth reentry speed of ~15km/s. That includes 30 days at Mars.

Most of the 2020 short duration missions all require entries back home ~19km/s, though. Short duration in 2022 all have 20km/s+ entires on return. 2031 is a good year to leave on a fast trip. Barely over a year total, and ~16km/s reentries.

Edited April 28, 2017 by tater

[sevenperforce]

1 hour ago, tater said:

OK, I figured out what I did. Set max duration to 2 years.

You can do a round trip Mars mission in the right years in under 400 days in 2018, 2033 with an Earth reentry speed of ~15km/s. That includes 30 days at Mars.

Most of the 2020 short duration missions all require entries back home ~19km/s, though. Short duration in 2022 all have 20km/s+ entires on return. 2031 is a good year to leave on a fast trip. Barely over a year total, and ~16km/s reentries.

How much dV do you need for the TMI, and how much dV do you need out of Martian orbit?

Trying to figure out whether it would be better to go ISRU-ahead or tanker only.

[tater]

4.41 km/s earth departure. 1.93km/s mars insertion, 4.15km/s mars departure. 18 km/s reentry velocity.

 

How big does a Mars transfer vehicle need to be? BA330 size for a 1 year trip? Bigger?

Edited April 28, 2017 by tater

[tater]

Any mission that minimizes duration is going to sacrifice free return. I have no idea what NASA safety requirements are, but many of the novel propulsion ideas are predicated on a non-free turn anyway (VASIMR, etc). So maybe they do a cost benefit on risk. Maybe a clustered engine system (so you can deal with engine outs by a longer burn), combined with the lower radiation exposure is worth the risk of a failure to insert at Mars. A departure failure is fatal, regardless. A failure in the middle of Mars orbital insertion is also fatal. Free return only buys you peace of mind if there is a failure after the TMI, but before you do anything else. Maybe it's mitigated by a 3X shorter trip.

Edited April 28, 2017 by tater

[sevenperforce]

45 minutes ago, tater said:

4.41 km/s earth departure. 1.93km/s mars insertion, 4.15km/s mars departure. 18 km/s reentry velocity.

How big does a Mars transfer vehicle need to be? BA330 size for a 1 year trip? Bigger?

Any mission that minimizes duration is going to sacrifice free return. I have no idea what NASA safety requirements are, but any of the over propulsion ideas are predicated on a non-free turn anyway (VASIMR, etc). So maybe they do a cost benefit on risk. Maybe a clustered engine system (so you can deal with engine outs by a longer burn), combined with the lower radiation exposure is worth the risk of a failure to insert at Mars. A departure failure is fatal, regardless. A failure in the middle of Mars orbital insertion is also fatal. Free return only buys you peace of mind if there is a failure after the TMI, but before you do anything else. Maybe it's mitigated by a 3X shorter trip.

Transfer vehicle size is a tricky thing. There's a minimum amount of physical activity space you're going to need to keep the crew from literally going crazy for any mission longer than a couple of weeks; the activity space is not necessarily going to go up very much based on mission duration. You're also going to need a certain amount of pressurized space to store consumables; this is going to increase significantly with mission duration.

Going expandable, like BA330, is the easiest way to get a big activity space. But you can't aerobrake an expandable module, and aerobraking is the only way you can do it without essentially doing a whole Mars Cycler.

My thought is that you build the activity space into something that can aerobrake, and use expandable modules (like BEAM) to store outgoing consumables. That way, you can doing a free-return on the outgoing leg, taking your sweet time to get to Mars, and then dump the expandable modules and aerobrake at Mars. You can then take a high-energy, low-transit-time return with as little mass as possible.

The mini-ITS concept I've been working on has a crew cabin volume of about 130 cubic meters. I was thinking they would go two at a time, each with two crew and a couple of BEAM modules docked in to store pressurized consumables, on a slow outgoing trip. Once at Mars, they'd dump the BEAMs, aerobrake, rendezvous, and transfer all but the barest fuel and consumables to the one remaining in orbit. The other vehicle would enter, land, complete the mission, and return to orbit. Both would refuel in orbit, using a previously-sent tanker or a previously-sent ISRU ship, and head home on the highest-energy transfer they could manage.

[shynung]

20 minutes ago, sevenperforce said:

But you can't aerobrake an expandable module

You can get around this by having a deflatable expandable module, and a rigid flight deck. Just before aerobraking, the crew goes to the flight deck and strap themselves, while the expandable module retracts (care must be taken to not leave free-floating items that may damage the module).

IDK if the BEAM module can be deflated and neatly folded after deployment, though. Might need some more development on that front.

[sevenperforce]

1 hour ago, shynung said:

You can get around this by having a deflatable expandable module, and a rigid flight deck. Just before aerobraking, the crew goes to the flight deck and strap themselves, while the expandable module retracts (care must be taken to not leave free-floating items that may damage the module).

IDK if the BEAM module can be deflated and neatly folded after deployment, though. Might need some more development on that front.

The BEAM's expansion is a onetime affair, so you'd need a complete redesign. Also, getting an expandable module inside an aeroshell is a tricky affair. The expandable module will have to be docked to a pressurized module while expanded, but will have to be deflated and removed from that module in order to be stowed inside an unpressurized cargo bay, but one which can be protected during aerobraking or re-entry.

[tater]

Or you bring the 2km/s worth of props.

[sevenperforce]

7 minutes ago, tater said:

Or you bring the 2km/s worth of props.

If you have a Martian Orbit Rendezvous mission architecture (the Mars equivalent of the LOR used by Apollo) and the ability to transfer propellant on orbit, there's a neat trick you can use to beat the rocket equation. Launch your service module, your expandable hab, and your lander/crew module into LEO, fuel them all, and dock them together. Use your service module's engines to perform the TMI.

Continue along your lazy transfer to Mars, making full use of your nice roomy hab. However, immediately before reaching Mars, physically transfer all your consumables from the hab into the lander. Disconnect the lander from the hab, and use the lander to aerocapture into low Martian orbit while the service module uses the last of its fuel reserves to do an orbital injection burn, still attached to the hab.

Once both the lander and the service module are in orbit, they can rendezvous and dock again. The lander will then transfer all but a few days' worth of consumables into the hab, and transfer all but the bare minimum of its fuel into the service module's tanks.

The lander then disconnects, enters, and lands. After the mission is complete, it returns to orbit with the last of its remaining fuel. It does a rendezvous with the hab and service module. All the remaining fuel from the service module is transferred back to the lander's tanks, and then the service module is jettisoned. The lander propels itself and the hab back to Earth with the same engines it used for Mars ascent.

In this way, you get the advantage of having an expandable hab on both legs of the journey, but you don't have to carry nearly as much propellant, because the propellant used for your return trip enters Mars orbit via aerocapture, but stays in Mars orbit in the service module's tanks while the lander executes its mission. Same with consumables.

[YNM]

Thanks for all the searching @tater ! Sounds nice at least at a glance (oh well yes it usually turns horrendous) ! Also interesting idead there from @sevenperforce !

I have to agree - most "modern take" on the whole problem (advanced propulsion systems) will in one way or another needs a non-failing set of engines. Not even you can have a "free return" in the cheapo ol' ways either (unless you're a space probe, which can simply be hibernated and put near the weird quasi-stable lagrangian points to travel around), so taking the risk of needing engines all the way is somewhat better than taking the risk of being a mutineer inside a space can, stranded years on trying to find (or waiting for) the right nudge that'll take you home.

So - is more propulsion a go ?

Edited April 28, 2017 by YNM

[tater]

I'd think that the engine out abort modes need to be reconsidered in a more aircraft way. Airliners have engine out capability. Spacecraft with multiple engines seems to make the most sense, and dump the free return. Use a Centaur, those things are pretty bulletproof.

 

Another goofy idea, and too kerbal for reality, but what the heck. If you used a LV with a good upper stage, and landing/reuse of that is a pain, why not reuse it in space. 

Instead of the mass required for landing S2, you make a similar adapter that is in fact designed for docking and propellant transfer. Note that it might require EVA, that's fine. The design might have the docking/transfer stuff exit to the side, so it's not a nose to nose type docking. You collect the stages where your craft is (say stuff you are sending ahead to Mars), and the upper stages are ganged to form a transfer stage for departure. At some point after they are connected and pressure tested, you send up tankers. You now have a few Merlin-1DV engines, or Be-4U engines as your departure stage.

[YNM]

20 minutes ago, tater said:

I'd think that the engine out abort modes need to be reconsidered in a more aircraft way. Airliners have engine out capability. Spacecraft with multiple engines seems to make the most sense, and dump the free return. Use a Centaur, those things are pretty bulletproof.

 

Another goofy idea, and too kerbal for reality, but what the heck. If you used a LV with a good upper stage, and landing/reuse of that is a pain, why not reuse it in space. 

Instead of the mass required for landing S2, you make a similar adapter that is in fact designed for docking and propellant transfer. Note that it might require EVA, that's fine. The design might have the docking/transfer stuff exit to the side, so it's not a nose to nose type docking. You collect the stages where your craft is (say stuff you are sending ahead to Mars), and the upper stages are ganged to form a transfer stage for departure. At some point after they are connected and pressure tested, you send up tankers. You now have a few Merlin-1DV engines, or Be-4U engines as your departure stage.

It's down to details I think. Someone should really contact NASA on this XD