Flight Question XR5 Round-trip cargo delivery mission to Mars without refueling on difficult/realistic settings

Marijn

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The plan is to transport as many standard AIA containers to Olympus Base as possible and return to KSC without refueling along the way. I've chosen a trajectory from NASA's Trajectory Browser in the near future optimizing for duration (lowest). Here's a screenshot of the plan: https://drive.google.com/file/d/1OheiDVcRP6ICR0gkfj1i0w3Gi-vpPYNS/view?usp=sharing

The plan is based on a parking orbit around Mars. Instead of entering a parking orbit, the final plan would need to include a landing on and launch from Mars.

For as much realism, I am considering these settings: MainFuelISP=1, LOXLoadout=1, LOXConsumptionRate=4, LOXConsumptionMultiplier=1.0, APUFuelBurnRate=4. Also, a full crew will be aboard and need to return to Earth alive.

My idea is aerobrake both at Mars and Earth arrivals without entering parking orbits, although the 21.17 km/s reentry speed at Earth arrival worries me a bit. Not sure if that's possible. And the amount APU fuel (49 minutes) seems to be a major problem and I might need to ease the burnrate to 3 (74min) or even 2 (110min) to have enough APU time for all the manouvres.

What do you think? Is this mission possible at all and if so, what would be the best strategy to deliver as many containers as possible? I like to hear your thoughts.
 

dbeachy1

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You may be able to do it if you reenter in multiple orbits, rather than all at once. You only need to set your periapsis on the initial Earth entry low enough to be captured by Earth's gravity (maybe 60 km or even higher?). Then you can set your apoapsis a bit lower on the next orbit to bleed off more energy until you can land. Be sure to change your orbital plane at apoapsis, though, to save fuel. (y)
 
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Marijn

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Thanks for the suggestion. So far, all my attempts failed spectacularly. I never got captured by earth. Either the ship burns up almost instantly or I stay on an hyperbolic trajectory without ever coming close to being captured. I tried PeA's of 70km, 75, 77.5, 80, 82.5, 85 and 90 while entering inverterted. But it doesn't seem possible.
 

Marijn

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Are you using Aerobrake MFD? That may help you.
Yes, I use Aerobrake MFD in the later stages of a landing. But it won't help in the very first stage when you hit the atmosphere. At least not as far as I know. But I am quite sure now reentering with 20km/s is simply not possible. Which is ok. I appreciate the realism.
 
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Buck Rogers

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13k playback

This is the fastest reentry I've acheived: Orbital V. at Pe: 13k+, PeA: 75k, ReA: ~1°, Ant.: ~90°, atmospheric contact with Mach 46+, XR2 although I speculate there's wiggle room for more I would say it's close to the limit, and with the XR5 I imagine even less.
 

Marijn

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This is the fastest reentry I've acheived: Orbital V. at Pe: 13k+, PeA: 75k, ReA: ~1°, Ant.: ~90°...
13k/s orbital velocity sounds doable. But it's still a costly burn to lower the speed when coming in at 20k+.

To stay within the contraints I described so far, I got the idea of splitting up the mission by bringing fuel and cargo to the moon first and then return to earth to pick up some more. Perhaps multiple of such trips. Then leave the moon for Mars with as many containers as possible and just enough fuel to make it to Mars and back to earth with an insertion burn which allows for a normal reentry.

But I am still wondering whether my failed attempts at reentering at 20km/s are due to me not being able to do it the right way or it is truely impossible due to physics.
 
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GLS

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Instead of direct entry, you could fly by the Moon and use it to slow down a bit... probably not much, but might be enough.
 

Buck Rogers

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I personnaly don't think 20k is viable, at 13k the reaction times are very small and it is certainly not an easy or very "safe" maneuver, not to say a computer controlled reentry couldn't produce better and safer results.
Your trajectory is optimized for lowest duration, i.e. max Dv, maybe it's possible to find a trajectory with a lower intercept velocity. I can recommend Trajectory Planner as a good tool for this.
As Debeachy1 stated; every time you touch the atmosphere you'll lower your apoapsis and eventually bring down your periapsis velocity, although this may extend your travel time by days or even months.
GLS's moonbrake and a Dv optimized trajectory may well give you acceptable parameters.
Good Luck & Godspeed, and pls post your results, I'd be interested to hear your solution.
 

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I don't think that a 20+ km/s Earth reentry is doable in an XR5. I calculate an altitude of ~78 km for a peak hull temp of 2800 C°. You'll probably won't be able to stay long enough at that altitude to lose much excess velocity., resulting in the Vanguard skipping back out to a hyperbolic trajectory.

Perhaps a different Earth-Mars-Earth trajectory is needed?

Here is an EVM-ME trajectory, (select the 1.88 yrs duration) launching on Sept 2023 with total time of 1.88 years (112 days is the stay on Mars). The Earth reentry is a relatively hard (but doable) 13.52 km/s

Untitled-1.jpg

The total dV is less than the plan you posted, but the time cost is ~9 months more. I don't know whether your constraints allow for no LOX consumption during the Mars stay, so there might be a problem if you need LOX for the time that the crew will be idling on Mars.

Would you mind sharing a start scenario and your XR5 config settings ?
 

Marijn

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Perhaps a different Earth-Mars-Earth trajectory is needed?
That looks like a better alternative. The crew will have to amuse themselves. And I like the Venus Flyby.

The replenishment of all consumables including LOX is disallowed. And only the containers included with the XR5Vanguard add-on are to be selected (the SCC cargo pack includes consumables with a better wet/dry mass ratio).

/config/MyXR5.xrcfg
[GENERAL]
MainFuelISP=1
LOXLoadout=1
LOXConsumptionRate=4
LOXConsumptionMultiplier=1.0
APUFuelBurnRate=4

But I am undecided about the APUFuelBurnRate. This setting may be too short for a launch and two aerobrakes.

I'll share the scenario here.
 

Marijn

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I am struggling to lift the XR5 off the deck after the 'rotate' callout, even when the takeoff-weight is well below the maximum according to the manual (572,225kg + 432,000kg = 1,004,225kg). Only below 800,000kg, I am able to lift off before running out of runway. I feel there's something wrong with this. The plane seems glued to the runway for some reason.

When using hover thrust as well, I can lift off well above the recommended max takeoff weight, even with all 36 cargo slots occupied.
 

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Perhaps gimballing the engines all the way up might help with that
 

Marijn

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Perhaps gimballing the engines all the way up might help with that
I tried that. But it doesn't help.

Fully loaded, but without cargo containers, I can't lift off below TAS=190m/s. On YouTube, I see liftoff's at 160m/s. After takeoff, I can slow down to below 130m/s and keep flying. Not sure what's going on. I also tried changing the ISP setting to check if that had something to do with it, but that doesn't seem to be the case.

I was planning on exceeding the max takeoff weight recommendation anyway, so it will be a hover engine assisted takeoff.
 

dgatsoulis

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I tried an ascent to orbit, fully loaded with AIA containers. That thing is sluggish as hell. Couldn't even get into a proper orbit (hardest settings possible for the XR5)
Full Crew of 18
MainFuelISP=0
SCRAMFuelISP=0
LOXLoadout=0
LOXConsumptionRate=4
LOXConsumptionMultiplier=1.0
MainEngineThrust=1
HoverEngineThrust=1
SCRAMfhv=1
SCRAMdmf=1
APUFuelBurnRate=5

Also couldn't get off the runway without a small assist from the hover engines. Barely managed to get into a 70x(-900) km suborbital trajectory. I really need to brush up on my XR5 ascend technique. Couple of questions for Marijn:

Where does the crew get its oxygen from during the stay on Mars? Is an external supply at Olympus ok? (not resupply, just zero oxygen use) or do they have to use the onboard oxygen?
Since you'll need at least a few cargo containers with consumables, is it ok to eject the used containers to save some mass, or not?

I can see your point about the APUFuelBurnRate. The launch to orbit on Earth takes more than 15 minutes. Even with extremely careful APU management, a setting of 5 might be impossible.
BTW, AerobrakeMFD can use the elevator trim without having the APU on, but that has always felt as cheating to me, so if I have the AerobrakeMFD "Hold" feature on, I also have the APU on.

Thanks for this interesting setup, I'll give it a try during the weekend and see how it goes.
 

Linguofreak

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I tried that. But it doesn't help.

Fully loaded, but without cargo containers, I can't lift off below TAS=190m/s. On YouTube, I see liftoff's at 160m/s. After takeoff, I can slow down to below 130m/s and keep flying. Not sure what's going on. I also tried changing the ISP setting to check if that had something to do with it, but that doesn't seem to be the case.

I was planning on exceeding the max takeoff weight recommendation anyway, so it will be a hover engine assisted takeoff.

The usual reason for rotation speeds far above stall speed (in any sort of aircraft, in real life or any sim) is a balance issue, namely, CG too far forward. If the CG is just in front of the main gear, the weight of the tail will just counterbalance the weight of the nose, and you won't have to go too fast to get sufficient elevator authority to rotate. If it's quite far ahead of the main gear, then the elevators will have to do most of the work to lift the nose on their own, with insufficient help from the weight of the tail.

If you have the opposite issue, it will be far too easy to rotate: in fact, you'll rotate at a TAS of 0, whether you want to or not (tl;dr "CG behind main gear, plane fall over backward, sit on tail").
 
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Marijn

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MainFuelISP=0
Are you sure setting it to 0 (expert)? I am planning on 1 which is labeled realistic.

-The crew has to use onboard oxygen until back on earth.
-Empty consumables can be deployed on any trajectory at any time and in any order. Burning with the bay doors open is not allowed.

Sounds good? Succes!
 

Marijn

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I am struggling with the return to earth part. As dictated by the Trajectory Browser, I am leaving at MJD 60616.5 and arrive at 60904.5, but IMFD's BaseApproach never gives me a solution. I wasn't able to work it out manually with the Map program either. So I am still working on a doable scenario before I share anything.
 

Marijn

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I am testing the return trip from Mars to earth first. I am having two problems. First, I can't reproduce the 1.72km/s delta-v for the eject burn to earth. The best solution I can find around the date 60616.5 is at least double the delta-v, around 3.450km/s.

The second problem is that I can't find a return trajectory which aligns me for a direct entry for Cape Canaveral. The 'Map Method' (Delta Velocity course program combines with the map) doesn't work in this situation. I think it's because the return trip crosses earth's orbit before the real encounter. It seems to me this messes up the possibility to use the map method. Not sure though.

Any help is much appreciated.
 
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