We need a new RLV - Moving beyond the shuttle

Shaun Barrett · 2003-02-08 19:29:03

I think there may be some confusion here.
The counterweight is out beyond GEO. The centre of gravity of the whole structure is kept at GEO distance - or, once the cable is firmly anchored (maybe difficult with a floating platform unless it's very heavy), the centre of gravity is shifted a little beyond GEO distance to keep the cable taut and allow for the weight of 'climbers' using it.
The maximum strain on the cable occurs at or near the GEO distance, which is where it needs to be strongest and hence thickest.

Ad Astra · 2003-03-10 21:52:24

Relegating the space elevator to the future when it's more feasible, the aerospace industry (or whatever's left of it, following the mergers and defense cutbacks of the 1990's) should concentrate on developing a commercially successful, unmanned RLV.

The natural market niche for this RLV is replacing the most successful commercial launcher of all time--the McDD Delta II. Of course, this would mean developing a relaible system on-the-cheap and operating it at a significantly cheaper price. The only alternative is if NASA and the USAF got together and said they wanted a new way to launch payloads under 5.8 tonnes.

My hope is that all ELVs will eventually be replaced by partially or fully-reusable launchers, operated by for-profit companies. Eventually, these reusable rockets will be man-rated and perform a plethora of tasks in makind's quest to tame space.

soph · 2003-03-10 21:54:58

AA: the SE will be built privately, by companies dedicated to the SE, not by the aerospace industry. So the two industries are not in comptetion, for the moment. And I think they will be able to exist in a supplemental relationship (i.e. SE cargo, RLV people/small cargo).

Josh Cryer · 2003-03-12 21:57:56

soph, RLV would be so cost-prohibitive that space elevators could easily take their place.

soph · 2003-03-13 05:27:03

Josh, there will always be a market for both. And I think RLV costs could be brought down tremendously.

The SE will take days to get to orbit, for people, a launch vehicle is far more desireable.

Josh Cryer · 2003-03-13 06:36:13

Far more desirable in the same way that flying Concord is far more desirable than flying third class in a jumbo...

I would be very surprised if RLVs could ever reach the price of an elevator. RLVs require so much freaking infrastructure, I'm afraid to even begin to list it. An elevator would only require maintenance that could only be done via robots, the thing would practically keep itself maintained.

I can maybe imagine personal RLVs, but they'd still be awfully expensive to run.

SpaceNut · 2016-06-21 21:31:34

Josh will need to fix his posts and I will fix the remaining

Who knew that we would be routting for a Reuseable Launch Vehicle...

Tom Kalbfus · 2016-06-22 06:00:57

SpaceNut wrote:

Josh will need to fix his posts and I will fix the remaining
Who knew that we would be routting for a Reuseable Launch Vehicle...

SpaceX is reusing a part of its vehicle. It seems easier to reuse a vehicle in pieces than to build an SSTO vehicle, unless you want to go nuclear! I find nothing wrong with a vehicle that comes apart to put a part of itself in orbit, and then has all of its pieces recovered, put back together and then reused. A space elevator, which I think he was talking about, has part of itself continuously in space, to deliver payloads to space, so we are waiting for someone with enough guts to build one. Maybe a Mars colonial transporter can deliver enough tonnage into orbit to drop down a space elevator, then we can really colonize Mars and other places!

Last edited by Tom Kalbfus (2016-06-22 06:03:52)

SpaceNut · 2016-06-22 17:31:13

With respect the reuseability there seems to be no need for the SSTO, Nuclear or a space elevator... just a plain ordinary rocket that can be even partially br reused seems to be enough of a game changer....

Tom Kalbfus · 2016-06-23 08:26:33

SpaceNut wrote:

With respect the reuseability there seems to be no need for the SSTO, Nuclear or a space elevator... just a plain ordinary rocket that can be even partially br reused seems to be enough of a game changer....

If you want something more than a research base with a handful of scientists, you will need complete reusability, you will want to expend nothing but fuel and energy, and not create junk and scrap all along the way. Now it would help if their pieces than came off could be retrieved and reused, instead of having to build replacement parts for each trip. The less we have to manufacture the less it will cost.

SpaceNut · 2016-06-24 20:11:03

Actually just cheaper prices to get bodies to there destination, reuseability is just one method to get a cheaper price.....

Tom Kalbfus · 2016-06-25 07:21:36

SpaceNut wrote:

Actually just cheaper prices to get bodies to there destination, reuseability is just one method to get a cheaper price.....

Imagine what a junkyard a Mars base would be if we used expendable landers to exchange crews there! That is the bottom stages of each MAV get left behind every time a crew returns to Earth. What's to be done with all that junk?

GW Johnson · 2016-06-25 09:00:16

Look, it's just using the rocket equation with available propulsion characteristics. Whether you enter Mars's atmosphere direct or from orbit, you come out of entry hypersonics at very low altitude moving pretty close to 0.7 km/s. It's too close to impact for chutes to do any good. So, you need 0.9 to maybe 1.0 km/s delta-vee capability to land.

Mars orbit speed is in the vicinity of 3.5 to 3.6 km/s, and there's almost no drag loss on a fast ascent trajectory. Gravity losses are weaker there, too. So, you need something in the neighborhood of 3.6 km/s delta-vee capability to reach Mars orbit. It makes little sense to try to go directly home, because the departure propellant is a huge deadhead mass penalty for both descent and ascent. Leave that stuff in Mars orbit.

The total velocity increment is around 4.5 km/s or close enough. If you 2-stage your lander, the descent stage actually needs a small mass ratio. Your ascent stage must provide the 3.6 km/s, and will be capable of little payload. It is the deadhead payload for the descent stage. Which means you can ship quite a bit down, but very little back up. And you only fly the vehicle once.

If you single-stage it, your down-payload capability is really mostly ascent propellant. At typical storable propellant capabilities, the useful down-payload will be around 3% of a 90-ton vehicle. But, if you don't push inert structure fractions too hard, you can do this in a vehicle that could fly the trip multiple times. That's a reusable landing boat, essentially.

Such a craft is quite voluminous. Use it for your surface habitation, instead of bringing along yet another thing that must also make the descent. Making it reusable leaves no hardware behind, and allows the enormous bang-for-the-buck multiplier of multiple trips.

The downside is shipping the propellant to Mars orbit to support those multiple trips, unless you can actually refuel the thing on the surface. Actually, prudence says ship some in case ISPP doesn't really work well enough, and then whatever ISPP you can pull off just adds more bang-for-the-buck.

If successfully refueled on the surface, the same vehicle then can bring down an enormous down-payload. Essentially the tonnage of the ascent propellant.

There's a real advantage to be had, basing from Mars orbit with a one-stage reusable lander like that, especially if effective ISPP is in place.

GW

Tom Kalbfus · 2016-06-25 15:20:05

I think its easier to bring stuff into Mars orbit from Earth, than to its surface. reusable stuff needs to be repaired and maintained, and the complex replacement parts will for a while have to come from Earth, as that is the only place they can be manufactured. You can refuel a reusable lander using a fuel plant to convert the atmosphere into fuel, but to maintain that fuel plant and the rocket engines, would probably be best done from orbit, if you want maximum use of that reusable equipment. Perhaps the interplanetary spaceship can be maintained in Low Earth orbit with stuff brought up from Earth. Complex technology is hard to produce locally after all.

SpaceNut · 2016-06-26 08:25:56

Tom Kalbfus you recycle the junkyard and make recycled rockets from the parts to be refueled from insitu resources with tanks being used for water, oxygen and fuel for later as excess is create of any of these if not used to make a rocket....

Tom Kalbfus · 2016-06-26 09:10:43

SpaceNut wrote:

Tom Kalbfus you recycle the junkyard and make recycled rockets from the parts to be refueled from insitu resources with tanks being used for water, oxygen and fuel for later as excess is create of any of these if not used to make a rocket....

Every time you exchange crews at the Mars base, you have more lander legs and bottom stages of vehicles left over, eventually there will be hundreds if this does not stop, the Mars base will be in the middle of a junkyard of used bottom stages of landers, and there will probably be a garbage dump nearby as well, all the cans and bottles imported from Earth.

GW Johnson · 2016-06-26 10:32:05

If you'll just bite the bullet and commit to a lander design too big to fit any existed or projected launch shrouds, you can build the one-stage lander right now. If your local propellant production proves successful, you can even ship down large masses with it. If not, at least you can ship down small masses with it.

Consider the lowest performing propellant because it is so storable: NTO and one of the hydrazines (all perform about the same). We're talking near-vacuum backpressures, so thrust performance is limited by practical geometric constraints on the engine bell expansion ratio. If 317 sec Isp is achievable (and it is), the corresponding exhaust velocity is about 3.109 km/s.

Assume for a reusable vehicle equipped with landing legs and a bail-out capsule an inert mass fraction of 0.20. Your velocity requirement is about 4.5 km/s for a 2-way trip. That corresponds to a required mass ratio of 4.252. That corresponds to a propellant fraction of 0.765. That leaves 0.035 as your payload fraction. If the vehicle is 90-100 ton size, you are looking at a 10 m dia heat shield, and a 3 to 3.5 ton down-payload (including crew). Fly less payload than that on ascent to leave a bit of maneuver margin.

If the retropropulsive landing delta-vee is 0.9 km/s, that mass ratio is 1.336, corresponding to a propellant fraction of 0.25, leaving the other .515 propellant fraction for ascent (when the vehicle is lighter). That means your ascent propellant is in the 46 to 52 ton range for that 90-100 ton vehicle.

If propellant manufacture on Mars proves successful, then the descent can load 3-3.5 tons plus 46-52 tons = 49 to 55 tons down payload, and still land fine. Refuel it on the surface, and it might take 3 tons back to orbit for you.

Now that's what the numbers look like for NTO-hydrazine. What they're talking about for propellant manufacture on Mars is LOX-LCH4, which has significantly better Isp potential, at least 10% better. That just makes all this look even more feasible.

A reusable vehicle that stages-off nothing and jettisons nothing. Made with stuff we already know how to do right now. Capable of landing men on Mars.

How come nobody is working on this?

The closest thing is Musk's Mars Colonial Transporter, I guess. And that's a ways off yet.

We do seem to have strayed far from the original topic: a reusable launch vehicle to replace the shuttle.

GW

Last edited by GW Johnson (2016-06-26 10:38:59)

Tom Kalbfus · 2016-06-26 11:02:02

They are much easier to make for Mars than for Earth.

RobertDyck · 2016-06-26 17:01:56

GW Johnson wrote:

What they're talking about for propellant manufacture on Mars is LOX-LCH4, which has significantly better Isp potential, at least 10% better. That just makes all this look even more feasible.

Zubrin got an SBIR contract from NASA years ago to build a brass-board demonstrator. It worked.

Next is unmanned demonstration on Mars. The Mars 2001 Lander was supposed to do that. It was cancelled after it's sister failed: Mars Polar Lander. It was "re-purposed" to become Mars Phoenix, but the In-Situ Propellant Production Precursor was removed. They removed all engineering experiments in favour of more science.

How come nobody is working on this?

We don't know what SpaceX is working on in back rooms. But mostly, no funding.

SpaceNut · 2016-06-26 20:47:23

Tom Kalbfus wrote:

SpaceNut wrote:
Tom Kalbfus you recycle the junkyard and make recycled rockets from the parts to be refueled from insitu resources with tanks being used for water, oxygen and fuel for later as excess is create of any of these if not used to make a rocket....
Every time you exchange crews at the Mars base, you have more lander legs and bottom stages of vehicles left over, eventually there will be hundreds if this does not stop, the Mars base will be in the middle of a junkyard of used bottom stages of landers, and there will probably be a garbage dump nearby as well, all the cans and bottles imported from Earth.

I guess recycling of the complete parts is not within the imagination. As I see the metal for creating new buildings and floor supports from the shell and legs....I see the ability to create tunnels with the metal lining to keep them from collapsing.....These would be idea for making barrier fencing for hill sides that might fall....
If we have fuel and oxydizer we have cutting torches to make them into anything we need.....

GW Johnson · 2016-06-27 08:47:53

A lot of such expended-stage stuff is aluminum. You cannot effectively work aluminum with oxyacetylene or any other torch gas combination. You'll need a saw or a water-jet cutter, and you'll need wire-feed inert-gas welding. The engines have both stainless steel and copper in them. But it's all in tube sweated or welded together. Salvage is not going to be as easy as we all would love to believe.

I knew about Zubrin's successful brassboard propellant-manufacture demonstrator. There's a lot of territory between a brassboard and a piece of operational equipment. And that territory is simply not covered by one lander experiment. Too many forget about that.

I just showed feasibility above, with the numbers for a chemical one-stage lander that could make multiple flights. I did it with NTO-MMH. The numbers are even better with LOX-LCH4. Why not sidestep the difficult salvage problem and just do this lander thing "right"?

If you can manufacture LOX-LCH4 in mass quantities quickly on Mars, then just use the lander to ship down the stuff you need for your facility, already in the form that you need it. You saw the tonnages I had estimated above. That's a lot of down-payload mass if you can refuel on the surface. But it's also a lot of tons of propellant.

That whole question rides of producing several dozen tons of propellants, on timescale preferably only months (or even only weeks) long. And THAT is why there is a whole lot of engineering development and test territory to cover between Zubrin's brassboard device and a useful propellant manufacturing plant on Mars.

GW

Last edited by GW Johnson (2016-06-27 09:00:08)

RobertDyck · 2016-06-28 08:15:46

The Sabatier reaction was used in the early 20th century to make "synthetic natural gas". The words "synthetic" and "natural" are an oxymoron, but they made methane. It was used for gas lamps, and other things. Industrial production.
Wikipedia: Sabatier reaction
Wikipedia: Gas lighting
Interior_Gas_Lighting_,_3_Light_Swan_neck_bracket..jpg

Zubrin's system uses the cold of Mars at night to harvest CO2 from atmosphere. Chilling atmosphere just a few degrees freezes dry ice. The warm to sublimate to form CO2 gas. The phase change self-pressurizes. His system brings LH2 from Earth. Industrial production requires a practical means to make hydrogen. That requires plentiful water and energy to split that for hydrogen.

Last edited by RobertDyck (2016-06-28 08:16:28)

GW Johnson · 2016-06-28 09:19:59

"Industrial production requires a practical means to make hydrogen. That requires plentiful water and energy to split that for hydrogen."

What that means is that you site the facility on top of a massive ice deposit (which is where, exactly, and "for sure"?). And you have to extract the water (steam down a well?) and deal with its mineral content (generalized salinity). I'm not sure any of that can be done by a robot lander.

You split the water and use the hydrogen and CO2 to make methane. Use the oxygen from the products and the water to make LOX. That's a propellant manufacturing plant. That's a lot of machinery, a lot of energy to operate it, and a super-strong need to be very site-adaptable as to water quality and its difficulty-to-extract.

So, any lander demonstrating methane manufacture is going to use a tank of LH2 brought from Earth. And you'll also have to bring the LOX to use with your methane. The LOX outweighs the LCH4 in most rocket designs, by far. I think the ratio is close to 4.

I conclude the robot lander demo of a sabatier rig is just one very small step along a rather long way to real propellant manufacture on Mars. I'd be very interested come September to find out how Musk intends to do this so quickly. Most of the speculations seem to indicate he wants to refuel his MCT (whatever that really is) on Mars with LOX and LCH4.

GW

Last edited by GW Johnson (2016-06-28 09:25:44)

RobertDyck · 2016-06-28 10:07:09

Oh, I'm sorry. I must have missed something. Mars Direct lands an ERV with LH2 brought from Earth. My plan is a modification of Mars Direct: it would use the same system for the MAV. I advocated a reusable rocket to hop around the planet only after a permanent human base is established. So human crews build and operate the propellant production facility, and that has to be demonstrated and operational before the reusable Mars shuttle is delivered. And I've posted before my belief (desire) that such a Mars shuttle would carry enough propellant to enter Mars orbit and return, to service an interplanetary craft parked in high Mars orbit. And the same craft would carry enough propellant for two suborbital hops without refuelling. One hop from base to a location of interest, then a return hop back.

I also said we should send an unmanned rover with a drill to test a potential location for that human base. To verify water ice is there. Initial human mission would not depend on that water for anything, but would leave habitat(s) and equipment to build-up a base.

GW Johnson · 2016-06-28 11:41:42

Well, my ancient Pratt & Whitney vest-pocket handbook lists the ratio of oxidizer to fuel for LOX-LCH4 as between 3.15 and 3.25, depending upon selected chamber pressure. That means for every ton of methane you make out of Martian air and LH2 brought from Earth, you will also need about 3.2 tons of LOX. Otherwise, your sabatier device only made 24% of the total propellant mass you need to run an engine. The other 76% is what I worry about.

If we're talking about bringing LH2 from Earth to demonstrate making methane on Mars, that's one thing. To actually use that methane, we're going to need LOX and lots of it. That means we split water, so it ain't just something based on Zubrin's sabatier device, it's a lot more. The trouble with Mars water is an awfully lot of it seems heavily contaminated with all sorts of salts. It takes just a dash of electrolyte to enable electrolysis; I'm unsure how that might work with electrolyte concentrations bordering on the saturated and ridiculous.

I understand we're talking about a permanent base that men have set up for real propellant manufacture. That will have a scaled-up sabatier for sure, and we will have an electrolysis plant making hydrogen and oxygen. I rather think we'll have some sort of mine or well recovering the raw dirty water, and a rather large and complicated water treatment plant to turn that raw water into something we can actually use.

I'm not saying this cannot be done, because it can be done. But it will not be easy, except in the rare case where the ice resource is actually fairly clean and fresh. I rather doubt that robots and remote-operated machines can do this, considering how different every site is going to be (just like here!).

What I find hard to accept is the notion (held by many) of doing this on the first landing and also counting on it for the means to get home. That sounds like a suicide mission to me.

GW

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#26 2003-02-08 19:29:03

Re: We need a new RLV - Moving beyond the shuttle

#27 2003-03-10 21:52:24

Re: We need a new RLV - Moving beyond the shuttle

#28 2003-03-10 21:54:58

Re: We need a new RLV - Moving beyond the shuttle

#29 2003-03-12 21:57:56

Re: We need a new RLV - Moving beyond the shuttle

#30 2003-03-13 05:27:03

Re: We need a new RLV - Moving beyond the shuttle

#31 2003-03-13 06:36:13

Re: We need a new RLV - Moving beyond the shuttle

#32 2016-06-21 21:31:34

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Re: We need a new RLV - Moving beyond the shuttle

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Re: We need a new RLV - Moving beyond the shuttle

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Re: We need a new RLV - Moving beyond the shuttle

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