Author Topic: Mars "domestic" launcher  (Read 7082 times)

Offline dwheeler

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Re: Mars "domestic" launcher
« Reply #20 on: 01/18/2018 01:48 AM »
I can't find any videos on YouTube of a CO/O2 rocket firing, which is my baseline for feasibility. Has one been built?
Yes, one was built like in the 1980s.


Not sure if this is what you were thinking of:

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19910014990.pdf

Quote
The results of the theoretical analysis indicate that a specific impulse in the range of 260 to 280 sec is realistic for the assumption of a low pressure engine. Specific impulses of 290 to 300 sec should be used, however, for the assumption of a higher pressure, pump-fed engine.

This was a 1991 study into using CO/O2 to fuel the return leg from Mars back to Earth.

Offline RoboGoofers

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Re: Mars "domestic" launcher
« Reply #21 on: 01/18/2018 03:39 AM »
Aerobraking to change a satellite's orbit has been done, but aerocapture into a planetary orbit has never been attempted - as far as I'm aware.

In an case, why would you bother? Just refuel on Mars and do whatever missions you want to do there. It's a fully reusable vehicle. Use it as many times as you need.

If you have ISRU already and lots of propellant.
I could see it being useful for a deployment of 'Marslink'.

As a technical point, BFS aerobraking into mars involves a point at which it's in a circular orbit. It just happens that this is 'deep' in the atmosphere.

It does require more knowledge of the atmospheric conditions. This could be a second BFS coming along six hours after the first though.
A issue with dropping them off after aerocapture is that they're in whatever orbit is convenient for BFS to land at it's destination. They would need large plane changes to get to useful inclinations. They also need to be sent fully fueled for this, reducing payload to surface.

Offline Robotbeat

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Re: Mars "domestic" launcher
« Reply #22 on: 01/18/2018 03:44 AM »
I can't find any videos on YouTube of a CO/O2 rocket firing, which is my baseline for feasibility. Has one been built?
Yes, one was built like in the 1980s.


Not sure if this is what you were thinking of:

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19910014990.pdf

Quote
The results of the theoretical analysis indicate that a specific impulse in the range of 260 to 280 sec is realistic for the assumption of a low pressure engine. Specific impulses of 290 to 300 sec should be used, however, for the assumption of a higher pressure, pump-fed engine.

This was a 1991 study into using CO/O2 to fuel the return leg from Mars back to Earth.
Precisely. An actual (very low performance) engine was built and tested.
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Offline Lar

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Re: Mars "domestic" launcher
« Reply #23 on: 01/18/2018 04:00 AM »
Many feel that some mesh of satellites for navigation and comms will be needed quite early, perhaps as soon as the second or even first landing. If these could be dropped off with a (very early) BFS on the way in, even if not in optimal orbits, is that helpful? A domestic launcher could well go get them later and reposition to better orbits.
"I think it would be great to be born on Earth and to die on Mars. Just hopefully not at the point of impact." -Elon Musk
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Offline Robotbeat

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Re: Mars "domestic" launcher
« Reply #24 on: 01/18/2018 04:21 AM »
If we're talking a BFR supplied colony, they'll already have to have methane ISRU up and running, so it seems the simplest solution would be to use existing infrastructure and methalox....
...simplest solution is to just use BFR. But BFR and any methalox launcher would be difficult to support in remote bases and wouldn't be as efficient.

Energy efficiency is a pretty big constraint. I calculate a full ITS tanker would take about 1 Megawatt for a two Earth years to fill up. And over a thousand tons of water. So any place on the planet you plan on traveling to either requires you to bring at least some of your return propellant with you (super inefficient energy-wise) or set up a significant mining operation. CO/O2 means you just need a big solar array (or nuclear reactor) and a big MOXIE with some liquifiers and tanks. Super easy to set up in any location you like.
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Offline speedevil

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Re: Mars "domestic" launcher
« Reply #25 on: 01/18/2018 05:56 AM »
I could see it being useful for a deployment of 'Marslink'.

As a technical point, BFS aerobraking into mars involves a point at which it's in a circular orbit. It just happens that this is 'deep' in the atmosphere.

It does require more knowledge of the atmospheric conditions. This could be a second BFS coming along six hours after the first though.
A issue with dropping them off after aerocapture is that they're in whatever orbit is convenient for BFS to land at it's destination. They would need large plane changes to get to useful inclinations. They also need to be sent fully fueled for this, reducing payload to surface.

It only reduces payload to surface if it either overloads the heatshield/aerosufaces and requires delta-v to keep it on a bearable trajectory, or the payload is volume constrained (in the case where you don't circularise the BFS after aerobrake).

If you are circularising after the initial aerobraking, then yes it will reduce payload to the surface, by the amount of the circularisation burn.

The circularisation burn is on the order of 70m/s, not 700m/s for landing, so it's perhaps 5-10 tons.

And if you were contemplating increasing the size of your ISRU before you'd have liked to, just to get up a minimal constellation, this may pay off immediately.

In principle, two BFRs can deploy a medium altitude constellation in two planes. Electric plane change isn't quite as terrible on earth, as LMO is 3.2km/s, not 7.8.

« Last Edit: 01/18/2018 06:01 AM by speedevil »

Offline RoboGoofers

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Re: Mars "domestic" launcher
« Reply #26 on: 01/18/2018 02:37 PM »
If we're talking a BFR supplied colony, they'll already have to have methane ISRU up and running, so it seems the simplest solution would be to use existing infrastructure and methalox....
Energy efficiency is a pretty big constraint. I calculate a full ITS tanker would take about 1 Megawatt for a two Earth years to fill up. And over a thousand tons of water. So any place on the planet you plan on traveling to either requires you to bring at least some of your return propellant with you (super inefficient energy-wise) or set up a significant mining operation. CO/O2 means you just need a big solar array (or nuclear reactor) and a big MOXIE with some liquifiers and tanks. Super easy to set up in any location you like.

So how long would it take to fill a F9-class mars rocket (15-20,000 kg to LMO) with CO and O2 at a remote site, and how much power would it require? How large would the tanks be, and what is the reentry profile.

we should not discuss the merits of different propellants and ISRU methods divorced from it's effect on the design of a rocket. You created another topic for CO/O2 already for that, which i'm reading through now.
https://forum.nasaspaceflight.com/index.php?topic=21544.0

If you want to build a rocket around CO/O2, that's great. Maybe someone prefers a CO2/Magnesium powder hybrid rocket. Hell, you can bring Kerosene if you want (i mean, please don't suggest this), but how does that decision effect the design of the rocket?
« Last Edit: 01/18/2018 02:54 PM by RoboGoofers »

Offline acsawdey

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Re: Mars "domestic" launcher
« Reply #27 on: 01/18/2018 04:25 PM »
So, poking around at a simple CO/O2 engine model in RPA lite. How does this sound for a little mars hopper/orbiter:

1 MPa chamber pressure (145 psi)
200:1 nozzle
0.52 O/F mixture ratio
270 isp at "optimum expansion" of 0.005 atm (~ mars surface?)
283 vac isp

With a super low chamber pressure, you could do this with electric pumps and very light weight tanks that just have enough pressure for the pumps to be happy.

If you crank the same thing to 10 MPa you'll get about 290-294 isp.

Offline Norm38

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Re: Mars "domestic" launcher
« Reply #28 on: 01/18/2018 04:57 PM »
Which uses less fuel, to allow a BFS to place cargo in Mars orbit?

1)  BFS makes a direct atmospheric entry, lands.  Then refuels and boosts back up into Mars orbit.

2)  A Mars supplied tanker lifts fuel to an orbital depot.  The BFS brakes into orbit, drops its cargo.  Refuels for landing, lands.

Offline RoboGoofers

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Re: Mars "domestic" launcher
« Reply #29 on: 01/18/2018 05:24 PM »
Is it logical to use this analogy: Using BFS on Mars for orbital launches is like using a BFR/S scaled 3 times larger to launch BFS payloads into LEO?

Offline Zed_Noir

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Re: Mars "domestic" launcher
« Reply #30 on: 01/18/2018 10:54 PM »
Is it logical to use this analogy: Using BFS on Mars for orbital launches is like using a BFR/S scaled 3 times larger to launch BFS payloads into LEO?

Yes. But you don't need to spend resources to developed and build another series of vehicles. That can only be used to and from the Martian surface with few other applications.

Of course if you have a few dozen spare billion dollars laying around, you might planned differently.

Offline speedevil

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Re: Mars "domestic" launcher
« Reply #31 on: 01/18/2018 11:04 PM »
Which uses less fuel, to allow a BFS to place cargo in Mars orbit?

1)  BFS makes a direct atmospheric entry, lands.  Then refuels and boosts back up into Mars orbit.

2)  A Mars supplied tanker lifts fuel to an orbital depot.  The BFS brakes into orbit, drops its cargo.  Refuels for landing, lands.

3) BFS aerobrakes into orbit, circularises, drops all its cargo, and lands.

Once you drop ~20 tons of cargo into orbit, you use enough less propellant on landing that you paid for the circularisation burn.
If you drop it all in orbit, you have quite a lot of propellant left over.
If you aerobrake into orbit, circularise, and refuel there, you can carry considerably more than 150 tons into orbit.

Circularisation takes of the order of 10 tons of fuel, landing 100, for the same initial heat loading on reentry, you can carry 250 tons of cargo to Mars (with 100t less propellant).

(edit: I wonder if I will ever stop typing fuel when I mean propellant)

« Last Edit: 01/18/2018 11:06 PM by speedevil »

Offline QuantumG

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Re: Mars "domestic" launcher
« Reply #32 on: 01/18/2018 11:09 PM »
3) BFS aerobrakes into orbit, circularises, drops all its cargo, and lands.

Aerocaptures into orbit. i.e., a manoeuvre that's never been done before by any spacecraft.

Why risk that when you can just land and refuel?
I hear those things are awfully loud. It glides as softly as a cloud. What's it called? Monowhale!

Offline speedevil

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Re: Mars "domestic" launcher
« Reply #33 on: 01/18/2018 11:18 PM »
3) BFS aerobrakes into orbit, circularises, drops all its cargo, and lands.

Aerocaptures into orbit. i.e., a manoeuvre that's never been done before by any spacecraft.

Why risk that when you can just land and refuel?

The risk for the first BFS with no atmospheric survey is probably too large.
However, if you can simulate landing, you can, with knowledge of the atmospheric density profile from a few minutes before (a small survey probe) simulate aerocapture - it is just a failed landing which does not curve hard enough into the atmosphere to remain in the deep part.

The question was what's the most efficient way - aerocapture is significantly more efficient to get payloads into orbit than launching them later in any way, and may be 'free'. (modulo uncertainty in trajectories due to poor knowledge of the atmosphere).

Hypersonic lifting reentry of a complex body  to vertical landing has never been done either.
The problems are basically the same as aerocapture.

Offline QuantumG

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Re: Mars "domestic" launcher
« Reply #34 on: 01/18/2018 11:30 PM »
Direct entry is vastly different to aerocapture. The degenerate case is getting to within 10 km of landing and then boosting again. It's completely unnecessary when you have a reusable vehicle and propellant sitting on the ground.

I hear those things are awfully loud. It glides as softly as a cloud. What's it called? Monowhale!

Offline speedevil

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Re: Mars "domestic" launcher
« Reply #35 on: 01/19/2018 12:27 AM »
Direct entry is vastly different to aerocapture. The degenerate case is getting to within 10 km of landing and then boosting again. It's completely unnecessary when you have a reusable vehicle and propellant sitting on the ground.
In what specific ways is it vastly different to aerocapture.
- from 35:53 in the IAC talk.

All the way down to 3km/s or so, BFS is positioned so that aerodynamic forces try to keep it in the atmosphere.
It does this precisely so that it does not skip off the atmosphere - it is actively forcing its trajectory down to keep it in the atmosphere at a downwards accelleration of about three times mars G at points.

As a first approximation, flip the lift vector from down round slowly to up at around 5km/s, and you end up in an elliptical orbit with an periapsis of some 35km, at a little more than LMO speed.
Precisely which elliptical orbit you end up in depends on the detailed trajectory design.
The heating is of a similar magnitude in the initial entry, and perhaps slightly less in the latter part to landing.

If you already have ISRU fuel on the ground, and have not well characterised the atmosphere, that is clearly the way to go.
« Last Edit: 01/19/2018 12:39 AM by speedevil »

Offline Robotbeat

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Re: Mars "domestic" launcher
« Reply #36 on: 01/19/2018 12:29 AM »
Yeah, I don't think aerocapture would be wildly difficult for BFS.
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Offline QuantumG

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Re: Mars "domestic" launcher
« Reply #37 on: 01/19/2018 12:42 AM »
Hypersonic manoeuvring is already a dicey proposition - but yeah, eventually anything is possible. So what?
I hear those things are awfully loud. It glides as softly as a cloud. What's it called? Monowhale!

Offline Lar

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Re: Mars "domestic" launcher
« Reply #38 on: 01/19/2018 12:50 AM »
Hypersonic manoeuvring is already a dicey proposition - but yeah, eventually anything is possible. So what?

(mod) No need to get so dicey, people are exploring the trade space, you already made your point that you think it's a bad idea.
« Last Edit: 01/19/2018 03:42 PM by Lar »
"I think it would be great to be born on Earth and to die on Mars. Just hopefully not at the point of impact." -Elon Musk
"We're a little bit like the dog who caught the bus" - Musk after CRS-8 S1 successfully landed on ASDS OCISLY

Offline Robotbeat

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Re: Mars "domestic" launcher
« Reply #39 on: 01/19/2018 01:12 AM »
Hypersonic manoeuvring is already a dicey proposition - but yeah, eventually anything is possible. So what?
Did you watch the animation of BFS hyperbolic entry on Mars? It's doing exactly that: precision hypersonic maneuvering: http://www.spacex.com/sites/spacex/files/mars-entry.mp4
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