Author Topic: HSF with small rockets  (Read 20712 times)

Offline spacenut

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Re: HSF with small rockets
« Reply #20 on: 10/15/2009 02:35 pm »
Skylon is what we should have built over the last 20 years instead of the existing space station.  Could have used international partners, would probably be back on the moon by now an working to assemble the Mars rocket. 

Why couldn't we use the empty Shuttle tanks and open one end for assembly or have it pressurized to work in shirt sleeve environment, then open the end to let out an assembled spacecraft?

With small rockets, one would need to develop a small nuclear engine capable of shuttle between Earth and Moon and then to mars. 

Offline Patchouli

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Re: HSF with small rockets
« Reply #21 on: 10/16/2009 02:05 am »
Skylon is what we should have built over the last 20 years instead of the existing space station.  Could have used international partners, would probably be back on the moon by now an working to assemble the Mars rocket. 

Why couldn't we use the empty Shuttle tanks and open one end for assembly or have it pressurized to work in shirt sleeve environment, then open the end to let out an assembled spacecraft?

With small rockets, one would need to develop a small nuclear engine capable of shuttle between Earth and Moon and then to mars. 

We should fund Skylon now but the technology to build it is fairly recent it wasn't possible until around the late 90s.
The heat exchanger technology for SABRE wasn't proven until last year though with more funding that would have happened a lot sooner.

Really anything in the sub 12T range in LEO should be carried by an RLV.

One thing we will have to do the get away from needing HLVs would be to learn how to perform low level assembly in space.
I'm talking going beyond simply docking things together and instead actually building things in space.
 
Such as welding or bolting together a hab module from metal plates on orbit.
ISS shows the limitations to small modules despite it's size it's cluttered and claustrophobic.

A crewed Mars mission is impossible with a 5M fairing even with inflatables the aeroshell just will not fit.
Inflatables only cuts the stowed size so much a 20 to 30M inflatable areoshell will probably still be over 5M packed.
You need to land something the size of a DOS station on Mars if you want a long surface visit and even larger if you want to crew to come back.
The LV for the MAV is probably going to have specs at least equal a Redstone or Falcon 1 rocket because Mars is still a pretty deep gravity well.
But most of the propellant for it can come from ISRU.
In theory a large aeroshell could be assembled in space but until that can be done an HLV may be needed.
« Last Edit: 10/16/2009 02:18 am by Patchouli »

Offline cgrunska

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Re: HSF with small rockets
« Reply #22 on: 10/16/2009 03:00 pm »
there's an orbital construction thread in advanced concepts.
I cant remember what the verdict was. I think it was cost prohibitive to  send all your materials up and have robots weld things together. Welding can be done i believe, but a shirtsleeve environment would not be practical for a while.


Offline mmeijeri

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Re: HSF with small rockets
« Reply #23 on: 10/16/2009 03:05 pm »
A crewed Mars mission is impossible with a 5M fairing even with inflatables the aeroshell just will not fit.

This is a myth. You don't need large payload fairings for Mars missions. You probably do need inflatables. With Mars the problem isn't descent but ascent. Bringing all your propellant with you would be prohibitively expensive. You would need ISRU for your ascent propellant, perhaps just on Phobos/Deimos, but probably on Mars itself.
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Offline Robotbeat

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Re: HSF with small rockets
« Reply #24 on: 10/16/2009 07:29 pm »
A crewed Mars mission is impossible with a 5M fairing even with inflatables the aeroshell just will not fit.

This is a myth. You don't need large payload fairings for Mars missions. You probably do need inflatables. With Mars the problem isn't descent but ascent. Bringing all your propellant with you would be prohibitively expensive. You would need ISRU for your ascent propellant, perhaps just on Phobos/Deimos, but probably on Mars itself.

If you're going to rely on ISRU for all your fuel, you can do a fully propulsive descent with your Mars ascent vehicle. No parachutes, no heatshield, no skycrane, etc.
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Offline mmeijeri

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Re: HSF with small rockets
« Reply #25 on: 10/16/2009 07:35 pm »
If you're going to rely on ISRU for all your fuel, you can do a fully propulsive descent with your Mars ascent vehicle. No parachutes, no heatshield, no skycrane, etc.

Exactly. We had some discussion about that on the Mars EDL technologies thread. And according to claims made there you'd only need about 2km/s of propulsive delta-v for the landing, the rest could be done with some form of aerodynamic deceleration, even without very large fairings.

BTW you don't strictly need ISRU for both descent and ascent. Descent propellant could be prepositioned by SEP. ISRU could be an optional upgrade. And if necessary a fleet of tugs could transport ISRU materials the other way too, so you wouldn't be wasting your investment.
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Offline Hop_David

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Re: HSF with small rockets
« Reply #26 on: 10/17/2009 03:32 pm »
-No space mission can go with 90% of it's peices.  An HLV mission delivers 50-100% of the mission in 1-2 shots.  The mission has a much more up or down launch success rate.  The only way you waiste both halves of the hardware is if the 1st launch is a success and the second is a failure.  All other situations you have either complete failure or success.

If you split your exploration mission into 4 pieces and the 1st 3 are successful, but the 4th fails, it's a LOM.  6 pieces and 1 failure LOM.  All modern LV are 95%+ reliable, whether they are small or large.  Small LV make your role the dice more.

Yes, I had made this point. But I didn't use the word LOM. I used "dead astronauts". Failure of any component will result in dead astronauts.


Is it possible to bust Apollo into enough chunks that each chunk can fit under the fairing of a Falcon 9? Or a Falcon 9 Heavy?

Of course it is.  But possible and optimal sometimes don't see eye to eye.  Some fun facts to remember when talking about the idea of large missions into small pieces.

I am beginning to think it's possible (if not optimal). However there are still some components I'm unsure of. For example, in his breaking of the Mars ERV into 6 chunks, he has something like the Apollo CSM. But this component must carry three astronauts for seven months and then enter's earth's neigbhorhood with a perigee velocity of 13 km/sec. I'm not sure the dry mass of this particular chunk could be lifted with an F9H.

-Unless using a VERY advanced tug, that has never been built,

The people I'm arguing with don't want to waste time with such tomfoolery, they want to go to Mars NOW. They also regard any non-Martian ISRU propellent a waste of time.

each piece will have to have it's own avionics, thrusters, and docking mechanisms.  If using a 20 MT launcher, that' 25% of your launch weight just to attach to the other pieces.

Here is my assessment of  delta V for landing stuff on Mars:

delta V for TMI from LEO is about 3.6 km/sec. Exiting Hohmann & landing on Mars is about 5.7 km/sec


Aerobraking can shed some of the 5.7 landing delta V. In my opinion, Zubrin tends to be optimistic. Aerobraking large payloads like habs would be more difficult than small payloads like rovers.


Shown above is a spectrum of possibilities for total delta V budget ranging from very optimistic to pessimistic.

But I admit I'm ignorant on Mars EDL. My WAG is 8 km/sec.

Does 8 km/sec mandate two stages?

If so, it seems to me each payload lofted to LEO must have two sets of thrusters and fuel tanks. Perhaps the lower stage could be a dumb stage guided by the avionics of the upper stage.

You are correct that avionics, thrusters, and docking mechanisms would subtract from useful mass landed on Mars surface. If two stages from LEO to Mars surface are needed. these will subtract even more. But I'm not sure how much.


-If launching all peices from one pad you will have a significant loiter time on your components.  If you use multiple pads you save on loiter time, but add new LOM possibilities due to pad delay.

Mars launch window lasts a couple of months, no? At this stage of the argument Zubrin's ERV has been busted into 6 chunks. How difficult is doing 6 launches in two month's time?

So far we haven't tried breaking apart Zubrin's other components but I wouldn't be surprised if those also bust 1 chunk into 6.

During the second launch window, astronauts as well as ERV chunks will be launched.

It seems to me this could require 12 launches in two month's time.

I support the idea of the Medium lift exploration system, it allows more balanced international cooperation, lower development costs, more immediate milestones, possibly lower costs, and greater synergy with commercial launch.  It's just not a panacea.

Yes, it seems like a more doable path to me for the reasons you mention. But it will take time to build infra structure that bring more ambitious goals within reach.

By trying to accomplish these goals NOW, I believe these advocates will actually push attainment further into the distant future.
« Last Edit: 10/17/2009 03:55 pm by Hop_David »

Offline A_M_Swallow

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Re: HSF with small rockets
« Reply #27 on: 10/17/2009 08:12 pm »
Mars launch window lasts a couple of months, no? At this stage of the argument Zubrin's ERV has been busted into 6 chunks. How difficult is doing 6 launches in two month's time?

If you have loiter time how about 6 launches in 6 months.  Much easier to manage.  Only the astronauts from Earth and departure from LEO needs to be in the 2 months window.

If you have 6 months to assemble the spacecraft there is time for a 7th launch to replace any component whose LV failed.

Offline Hop_David

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Re: HSF with small rockets
« Reply #28 on: 10/17/2009 09:29 pm »

If you have loiter time how about 6 launches in 6 months.  Much easier to manage.  Only the astronauts from Earth and departure from LEO needs to be in the 2 months window.

If you have 6 months to assemble the spacecraft there is time for a 7th launch to replace any component whose LV failed.

The payloads destined for Mars surface loitering in LEO would need enough propellent for 8 km/sec delta V, I believe.

How would you power the refrigeration units on the Lh2 tanks for 6 months? will you have a shield that protects the Lh2 tanks from the sun's light as well as reflected sunlight from earth's oceans?

Or would you do separate launches to fuel propellent depots to serve the loitering Mars bound mass?

Offline mmeijeri

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Re: HSF with small rockets
« Reply #29 on: 10/17/2009 09:30 pm »
Why are we assuming the TMI is done from LEO? Using L1/L2 is much easier, especially with small rockets.
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Offline Hop_David

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Re: HSF with small rockets
« Reply #30 on: 10/17/2009 10:44 pm »
Why are we assuming the TMI is done from LEO? Using L1/L2 is much easier, especially with small rockets.

Part of my motivation for this thread was to better inform myself for a discussion on a New Mars thread Budgeting for a Mission

Some of the people I'm arguing with at that forum adhere to the orthodox Zubrin doctrine that the moon, EML1, etc. are silly distractions. They seem to believe that if we stopped wasting our time and money on such shenanigans that we would be well on way to establishing a self sufficient Martian colony. So I was working within their architecture.

But you are correct, a small rocket architecture sans EML1 and 2 isn't a topic of much interest in this forum.
« Last Edit: 10/17/2009 10:46 pm by Hop_David »

Offline A_M_Swallow

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Re: HSF with small rockets
« Reply #31 on: 10/17/2009 11:24 pm »

If you have loiter time how about 6 launches in 6 months.  Much easier to manage.  Only the astronauts from Earth and departure from LEO needs to be in the 2 months window.

If you have 6 months to assemble the spacecraft there is time for a 7th launch to replace any component whose LV failed.


The payloads destined for Mars surface loitering in LEO would need enough propellent for 8 km/sec delta V, I believe.

How would you power the refrigeration units on the Lh2 tanks for 6 months? will you have a shield that protects the Lh2 tanks from the sun's light as well as reflected sunlight from earth's oceans?

Or would you do separate launches to fuel propellent depots to serve the loitering Mars bound mass?

I suspect that a Mars transfer vehicle will need a sunshield and refrigeration unit to protect the return fuel.  Putting the fuel into a solar electric powered depot whilst the vehicle is assembled is a reasonable solution to the LEO boil-off problem.  The depot can be reused on future flights.

Offline kkattula

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Re: HSF with small rockets
« Reply #32 on: 10/18/2009 04:31 am »
If you're going with an EML2 (better than EML1 for Mars) staging point, it might as well be a dedicated depot so your TMI propulsion stages don't have to carry the mass required to store the propellant for up to 6 months.

Equally you might as well return to EML2 from Mars, rather than have to carry an Earth entry heat shield there and back. The propulsive requirement to insert back into EML2 is likely less than the mass of that heatshield.

And if you have already developed the depot and related architecture, why not put another depot in Mars orbit or Sun Mars L1?

Suddenly all you delta v 'stages' become very manageable, and medium LV flight rates go way up, bring on reduced per flight costs.

Win-Win.

Offline mmeijeri

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Re: HSF with small rockets
« Reply #33 on: 10/18/2009 12:12 pm »
Exactly. Because I don't like putting unproven technologies like long term cryogenic storage and cryogenic propellant transfer on the critical path I would want to start with hypergolics from L1/L2 (but cryogenics from LEO to L1/L2). This is well within the delta-v range of a reusable moon lander (4-5km/s) and completely eliminates boil-off issues at a stroke. If you do this, an SML-1 depot becomes more important for efficiency/trip time. To avoid the need for aerobraking into Mars orbit (more unproven technology) and to reduce the cost of propulsive braking, you could brake into a very high Mars orbit. You could then also use more delta-v to arrive sooner so you are not exposed to GCR (big risk) for a long time. If you refuel at SML-1, you can use SEP to preposition your propellant, which would increase efficiency a lot.
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Offline mmeijeri

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Re: HSF with small rockets
« Reply #34 on: 10/18/2009 01:30 pm »
Part of my motivation for this thread was to better inform myself for a discussion on a New Mars thread Budgeting for a Mission

Thanks for that link, I'll go have a look.

Quote
Some of the people I'm arguing with at that forum adhere to the orthodox Zubrin doctrine that the moon, EML1, etc. are silly distractions. They seem to believe that if we stopped wasting our time and money on such shenanigans that we would be well on way to establishing a self sufficient Martian colony. So I was working within their architecture.

I'd be interested to know what Zubrin would think of EELVs + Lagrange point hypergolic refueling + SEP. Some of this is similar to things he has proposed in the past with Athena. He's big on proven technology and doing things soon, so who knows.
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Offline meiza

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Re: HSF with small rockets
« Reply #35 on: 10/18/2009 02:14 pm »
Could you use a space tether to throw payloads / propellant from LEO to SEL-1 or EML-2? This could avoid space tugs that have to go through van Allen belts.
How much delta vee do you need to start the transfer to SEL-1 and then to "stop" there?

Offline mmeijeri

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Re: HSF with small rockets
« Reply #36 on: 10/18/2009 02:19 pm »
I suspect a tether is more difficult than a tug crossing the van Allens repeatedly. While current technology doesn't allow that yet, CIGS panels or Stirling engines capable of doing that may be on the horizon.

Braking into EML-1 is roughly 0.6km/s for a normal trajectory, SEL-2 should be less. But there even exist ballistic three body trajectories that need no insertion burn, just a slightly larger TLI. You would still need small corrections, but no more than that.
« Last Edit: 10/18/2009 02:19 pm by mmeijeri »
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Offline robertross

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Re: HSF with small rockets
« Reply #37 on: 10/18/2009 03:06 pm »
Part of my motivation for this thread was to better inform myself for a discussion on a New Mars thread Budgeting for a Mission

Thanks for that link, I'll go have a look.


I'll second that. Thanks for the link. More reading...lol

Offline kkattula

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Re: HSF with small rockets
« Reply #38 on: 10/18/2009 06:33 pm »
In my view if you can't do long term cryogenic storage and cryogenic propellant transfer, you have no business going to Mars.

This should help:

http://www.ulalaunch.com/docs/publications/CryogenicOrbitalTestbed(CRYOTE)2009.pdf

"CRYOTE can increase component and system TRL to Level 7."

Offline Robotbeat

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Re: HSF with small rockets
« Reply #39 on: 10/18/2009 07:21 pm »
In my view if you can't do long term cryogenic storage and cryogenic propellant transfer, you have no business going to Mars.

This should help:

http://www.ulalaunch.com/docs/publications/CryogenicOrbitalTestbed(CRYOTE)2009.pdf

"CRYOTE can increase component and system TRL to Level 7."

I agree, but soft cryogenics.  Hard cryogenics (hydrogen) are considerably harder and can be replaced with methalox (is that a term?) and/or kerolox if hard cryogenics are too challenging. You need liquid oxygen for crew consumption, don't you?
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