So I have an Idea... SSTOs to mars.

[DerpenWolf]

NOTE: For some reason everyone is thinking that this would involve sending men to mars... it doesn't, it involves sending satellites, food, experiments and the like so please stop yelling at me about how the concept is likely unfeasible for manned spaceflight, I already knew that!!!!!!

Basic Stuff:

-So you need about 8-9k m/s of velocity change to get into orbit right? Well, after doing a bit of research I've found out that that is roughly what is required to go to mars and to come back on rocket power... light aerobraking can be done though it is best for it to be avoided to prevent wear and tear on your reentry system.

The plan:

-Lets say we have a SSTO like the X-33 concept that runs entirely on rockets the whole journey, you could essentially put one of these spacecraft in orbit, refuel it with another SSTO, and send it to mars with its payload and have it come back... Yes I understand you would need to make sure your systems would function over the duration of the trip but this could prove to be an interesting way SSTO's could deliver interplanetary payloads without in orbit assembly or the need to design the vehicle that would be preforming the transfer! So in layman's terms you refuel an SSTO in orbit, send it into a mars orbit, have it deploy its payload, then the SSTO returns to earth to be reused...

Just one of my many ideas, Be sure to tell me what you think!

Edited August 19, 2014 by DerpenWolf

[rtxoff]

And who is going to sit all the years in the cockpit as long as the mission lasts? Also life support for such a long mission would weight more then a feasable payload of such an SSTO. Real life is not KSP.

[Streetwind]

Real-life SSTOs have abysmally low payload allowance due to the fuel mass fractions required to make them work.

I'm not saying it won't ever be possible as our technology advances, but the thing to remember right now is: SSTOs don't exist. Not a single such vehicle has ever been built and flown. No craft we have ever launched made it into a stable orbit around Earth without staging. There were a few concepts that potentially could have done it, but nobody wanted to build them because they had no payload capacity worth mentioning, and thus no business case.

At bare minimum you'd have to wait for Skylon to fly. That's the only vehicle currently in planning that has a reasonable shot at being single stage to orbit without being practically useless at the same time. Assuming it ever flies, it will be sometime in the 20's. Payload will be lower than that of a staged rocket still, but the reusable spaceplane concept should theoretically allow it to remain cost competitive. Theoretically. Reaction Systems has a ton of work left to do to prove their concept viable. And if reusable rocket stages are mainstream by then, it might simply stop being cost competitive again.

As advances in technology make SSTOs better, they also make staged vehicles better. And staged vehicles are pretty much always better.

Edited August 19, 2014 by Streetwind

[Nibb31]

Going to Mars isn't just about dV. You can't just take a Soyuz or a Space Shuttle and send it to Mars. You also need supplies, power, durability, and radiation shielding.

First of all, the X-33 was never meant to be manned, or even orbital. It was a suborbital test demonstrator for VentureStar. VentureStar was to have similar capabilities to the Space Shuttle. This means that it would have been able to stay in orbit for a week or so. After that, all systems would be dead. It couldn't carry the supplies, the fuel, the solar arrays, the shielding, and the habitation volume for a Mars trip. In real-life, SSTO has a terrible payload fraction.

You wouldn't want to explore the jungle in a Mini, and a Range Rover isn't the best vehicle for your grocery runs. Building deep-space exploration spacecraft and a LEO taxi are two different things. This is why NASA is building Orion and running the CCDev program at the same time, because Orion would be too expensive as a LEO taxi, and Dragon/CST-100/DreamChaser would be crap for deep space exploration. Different vehicles for different purposes.

Edited August 19, 2014 by Nibb31

[DerpenWolf]

And who is going to sit all the years in the cockpit as long as the mission lasts? Also life support for such a long mission would weight more then a feasable payload of such an SSTO. Real life is not KSP.

I said payload, I never said people would be riding in this... They could technically fit under the classification of payload though I would still not advise riding in the spacecraft. This would be largely used for delivering equipment, food, and satellites to the mars system on the cheap .

Real-life SSTOs have abysmally low payload allowance due to the fuel mass fractions required to make them work.

I'm not saying it won't ever be possible as our technology advances, but the thing to remember right now is: SSTOs don't exist. Not a single such vehicle has ever been built and flown. No craft we have ever launched made it into a stable orbit around Earth without staging. There were a few concepts that potentially could have done it, but nobody wanted to build them because they had no payload capacity worth mentioning, and thus no business case.

At bare minimum you'd have to wait for Skylon to fly. That's the only vehicle currently in planning that has a reasonable shot at being single stage to orbit without being practically useless at the same time. Assuming it ever flies, it will be sometime in the 20's. Payload will be lower than that of a staged rocket still, but the reusable spaceplane concept should theoretically allow it to remain cost competitive. Theoretically. Reaction Systems has a ton of work left to do to prove their concept viable. And if reusable rocket stages are mainstream by then, it might simply stop being cost competitive again.

As advances in technology make SSTOs better, they also make staged vehicles better. And staged vehicles are pretty much always better.

Well we better build a big spacecraft then! But really we do know that it is possible to build a earth SSTO, the main problem though is really that few are willing to make the investment and build the vehicle... Though when you think about it if you have a SSTO that can only lift 7 tons to orbit on a full tank of gas your payload to mars is still 7 tons after you refuel as the velocity change you are capable of remains the same on a full tank.

[DerpenWolf]

Going to Mars isn't just about dV. You can't just take a Soyuz or a Space Shuttle and send it to Mars. You also need supplies, power, durability, and radiation shielding.

First of all, the X-33 was never meant to be manned, or even orbital. It was a suborbital test demonstrator for VentureStar. VentureStar was to have similar capabilities to the Space Shuttle. This means that it would have been able to stay in orbit for a week or so. After that, all systems would be dead. It couldn't carry the supplies, the fuel, the solar arrays, the shielding, and the habitation volume for a Mars trip. In real-life, SSTO has a terrible payload fraction.

You wouldn't want to explore the jungle in a Mini, and a Range Rover isn't the best vehicle for your grocery runs. Building deep-space exploration spacecraft and a LEO taxi are two different things. This is why NASA is building Orion and running the CCDev program at the same time, because Orion would be too expensive as a LEO taxi, and Dragon/CST-100/DreamChaser would be crap for deep space exploration. Different vehicles for different purposes.

I never said it would send people... The concept just involves sending satellites, snacks, and the like to mars... I used the X-33 as an example as the concept ran entirely on rocket engines meaning it doesn't have jet engines that would reduce the need to have as much fuel for rocket mode, meaning as much vacuum useable fuel as possible...

[Nibb31]

It's possible to build an SSTO, but the payload fraction is useless.

But what is the point of building an SSTO to take 7 tons to Mars if it isn't coming back? It would be expended anyway, so you're just building a heavier rocket and wasting a lot of payload and expensive reusable hardware that isn't needed. It would take two launches and be more expensive than using a conventional multi-stage rocket.

[DerpenWolf]

It's possible to build an SSTO, but the payload fraction is useless.

But what is the point of building an SSTO to take 7 tons to Mars if it isn't coming back? It would be expended anyway, so you're just building a heavier rocket and wasting a lot of payload and expensive reusable hardware that isn't needed. It would take two launches and be more expensive than using a conventional multi-stage rocket.

THE POINT IS THAT THE SSTO CAN COME BACK, BE REFUELED AND REUSED... The point is nothing gets thrown away. I probably should do some serious clarification on the main post if people are this confused..

Edited August 19, 2014 by DerpenWolf

[Streetwind]

I think what you really want is a space tug.

A robotic vehicle is placed into Earth orbit. This vehicle has an extremely efficient proulsion system. You then launch a payload module and dock it to the tug, which takes the payload to Mars and then returns to Earth (or waits for the payload to do its job at Mars and then takes it back to Earth). Afterwards you refuel the tug with fuel refined in space (asteroid mining) or launched from Earth by something that can, if you really want to, be a SSTO of some description. Skylon might be able to carry enough, who knows.

Pure space vehicles can be built much more efficiently than something launched directly from Earth, especially if they're robotic craft. They don't need to be built to land and launch repeatedly, they don't need to handle atmospheres, they don't need to support life. All they need to be is an engine, a fuel tank, a power source, a control computer and a docking collar strutted together in a suitable way. Such a tug can be launched by a conventional SHL rocket (like the Falcon Heavy or the SLS); a small one might even be able to go on the Delta IV Heavy. It takes just one launch, and then it stays up there for however many trips you want to take to whatever places you desire (provided you can refuel it). And also: what the payload section you tug to Mars actually is, or what it does there, is irrelevant to the tug. It just tugs stuff. Anyone can attach anything to it so long as it has the proper matching docking port.

Also, if it can go to Mars, it could also go to Venus. In fact, if it was running solar electric propulsion, it would be even better suited for going to Venus than for going to Mars.

Edited August 19, 2014 by Streetwind

[Nibb31]

THE POINT IS THAT THE SSTO CAN COME BACK, BE REFUELED AND REUSED... The point is nothing gets thrown away. I probably should do some serious clarification on the main post if people are this confused..

If reusability is your goal, then who cares if it's SSTO or MSTO. Multiple stages will give you a much higher payload and potentially allow a single launch instead of "lots".

On paper, if it had worked as designed, VentureStar was to have a LEO payload capability of ~20 tons. The vehicle itself would have weighed around 100 tons, and it would have carried 900 tons of propellant. This means that your second VentureStar would need to fly at least 45 refueling missions to fill up the first VentureStar. In reality, these 45 launches would have to be done over a period of a few days because of propellant boiloff, or you would need even more launches to compensate for lost propellant, which makes the whole thing unfeasible.

VentureStar was designed for LEO missions and not for interplanetary missions. It would need extensive modifications to turn it into a decent MTV, including a whole new power source and supplies for expendables. These modifications would seriously cut into the 20 ton payload capacity.

And once it arrives at Mars, what next? It wouldn't have enough dV to also do an orbital insertion, so it would have to go for a direct reentry and somehow refuel on Mars, but wings designed for Earth's atmosphere don't work too well on Mars, so it would also need to do a propulsive landing, which requires even more modifications.

In the end, you are better off designing a vehicle built for the purpose rather than sticking floats on a Land Rover to get it to cross the Atlantic.

Purpose built means that you would have your reusable LEO taxi (SSTO or MSTO, who cares?) with high-thrust engines, your reusable MTV with low-thrust/high ISP vacuum engines (SEP or NTR) for the interplanetary transfer, and your reusable MAV for shuttling between LMO and the base.

Edited August 19, 2014 by Nibb31

[DerpenWolf]

I think what you really want is a space tug.

A robotic vehicle is placed into Earth orbit. This vehicle has an extremely efficient proulsion system. You then launch a payload module and dock it to the tug, which takes the payload to Mars and then returns to Earth (or waits for the payload to do its job at Mars and then takes it back to Earth). Afterwards you refuel the tug with fuel refined in space (asteroid mining) or launched from Earth by something that can, if you really want to, be a SSTO of some description. Skylon might be able to carry enough, who knows.

Pure space vehicles can be built much more efficiently than something launched directly from Earth, especially if they're robotic craft. They don't need to be built to land and launch repeatedly, they don't need to handle atmospheres, they don't need to support life. All they need to be is an engine, a fuel tank, a power source, a control computer and a docking collar bolted together in a suitable way. Such a tug can be launched by a conventional SHL rocket (like the Falcon Heavy or the SLS); a small one might even be able to go on the Delta IV Heavy. It takes just one launch, and then it stays up there for however many trips you want to take to whatever places you desire (provided you can refuel it). And also: what the payload section you tug to Mars actually is, or what it does there, is irrelevant to the tug. It just tugs stuff. Anyone can attach anything to it so long as it has the proper matching docking port.

Huzza! Someone understood what I was attempting to explain!! But yea, I really should put unmanned space tug in the original post, as it is an excellent way of helping explain the concept! But yea, I know that a vehicle designed to be a tug would probably work better but the big idea behind reusing a SSTO for this task is that you don't need to spend the money designing and building said tug if your company is short on cash!

[Nibb31]

If you're short on cash, building a purpose-built space tug will be cheaper than turning a spaceplane into a space tug.

[Streetwind]

If you are short on cash, then you wouldn't be dabbling in SSTOs, because they're incredibly expensive to develop

Unless there was a different company from which you can charter the transportation service. Then it becomes a question of how much payload you have, in what blocks you can divide said payload, and how many SSTO spaceplane flights you'd have to purchase to get it all into orbit versus buying a single (semi-)expendable staged launcher. But on the other hand, if you were chartering a different company's launch vehicle, then you couldn't refuel it in orbit and send it to Mars.

I mean, I see your point of the convenient similarity of "dV required to launch into low earth orbit equals dV required to fly Mars return mission". But anything built as an Earth ascent vehicle would be useless for a deep space mission, even a robotic one. It will not be built for orbital refueling. It will not carry a power source. It will not carry the high gain communications antenna required to receive commands from Earth and send telemetry and research data. It could only carry a tiny fraction of the payload of a dedicated space tug (or even a dedicated conventional spacecraft). It would not have radiation shielding - believe it or not, even electronics need to be shielded outside the Van Allen belt. And that's just the tip of the iceberg.

Your dV comparison in this case may be correct, but it doesn't mean anything if the vehicle is impractical. One could just as well make a comparison like: "it just so happens that the fuel required for a combine harvester to mow a maximum size wheat field is pretty much the same as the fuel required to go the distance in this touring cup race". So why not use a combine harvester to drive in the touring cup race? It absolutely can go the distance, nobody questions the technical feasibility. But that doesn't change the fact that a combine harvester is an utterly terrible choice of vehicle for driving in a touring cup race... even if you are short on cash. And a touring race car is also cheaper than a combine harvester.

Edited August 19, 2014 by Streetwind

[sgt_flyer]

Current SSTO designs all use LH2-lox fuels + oxydizer. Those fuels are not adapted for long duration space activities - because they are cryogenic, you would need to maintain ultra low temperatures at all time, + you'll still have boil-off (and h2 porosity)

Besides, ssto designs require turbopumps, which are less reliable than pressure fed systems.

As others pointed out, a reusable space tug with hypergolics would be a much more interesting approach - and you can still send an SSTO to refuel it if you want. (And you'll save on mass fraction of the tug, as it won't need to haul around all the hull / tps of the reusable SSTO's.

[Red Iron Crown]

It still has yet to be demonstrated that a reusable surface-LEO spacecraft can be made with a lower per-launch cost than a conventional disposable. Real life is not like KSP, it's not as simple as just filling the tanks and taxiing back to the runway. We've had the technology to make an SSTO for decades, it just hasn't been viable to do so.

As for reusing the ascent vehicle for exploring Mars, that's grossly oversimplifying the challenges involved down to KSP levels. All that atmospheric equipment and high TWR is wasted going to Mars, and a surface-LEO shuttle doesn't need and shouldn't carry a support system capable of the months needed for a Mars trip. A specialized ship for each task is the way to go, as Nibb31 mentions. No compromises trying to multimission the ship, and each of these specialized craft can be reusable if that can be made desirable.

[KerikBalm]

THE POINT IS THAT THE SSTO CAN COME BACK, BE REFUELED AND REUSED... The point is nothing gets thrown away. I probably should do some serious clarification on the main post if people are this confused..

Except a whole lot of reaction mass, of course.

SSTOs don't exist. Not a single such vehicle has ever been built and flown. No craft we have ever launched made it into a stable orbit around Earth without staging.

I don't think that is true. Quite a few launchers can be SSTO with a tiny payload.

Its when you try to make them reusable that you run into problems. I seem to recall hearing that there were some test of launchers that basically ended up being SSTO with no payloads.

More generally, this thread is about a reusable transfer vehicle to Mars... not a new concept.

I still think something "shuttle like" would probably be the most cost effective way of getting into orbit -> uses staging, but parts are recoverable.

SpaceX seems to be getting close.

[R0cketC0der]

The maximum specific impulse that can be obtained with hydrolox is IIRC 463 seconds. The delta-V needed for getting the low mars orbit and back from earth surface is about 16.5km/s, if all aerobraking maneuvers possible get done. This means in ideal circumstances, not counting the reduced efficiency inside earths atmosphere, about 97.4% of the vehicles mass need to be fuel. AFAIK the best fuel fraction ever achieved for a fuel tank was 96% for the space shuttle ET. This means that even if your engine, heatshield, communications, etc. would weigh nothing, it would still be impossible with today's technology. And this isn't even accounting for cryogenic boil off and a lot of other problems with it.

Edited August 20, 2014 by R0cketC0der

[Streetwind]

I seem to recall hearing that there were some test of launchers that basically ended up being SSTO with no payloads.

Got some source on this? I'm very interested in this kind of thing.

The maximum specific impulse that can be obtained with hydrolox is IIRC 463 seconds.

The RL10-B2 engine used on the Delta IV Heavy upper stage claims a specific impulse of somewhere around this figure, I've seen it quoted anywhere between 462 and 464. That said, though, it seems more a limitation of engine technology and not one of the hydrolox reaction. For instance, that is an expander cycle engine. Those are fairly efficient, but maybe a full flow staged combustion design could achieve slightly higher chamber pressures, increasing Isp to 465-470s?

What I mean to say is, your statement would be more correct if it said "the maximum specific impulse that has been obtained with hydrolox so far".

The delta-V needed for getting the low mars obesity and back from earth surface is about 16.5km/s

Posting from mobile, are we?

Just want to point out that DerpenWolf's post is specifically not about dV from Earth surface. He wants to refuel in Earth orbit.

[Nibb31]

The maximum specific impulse that can be obtained with hydrolox is IIRC 463 seconds. The delta-V needed for getting the low mars obesity and back from earth surface is about 16.5km/s, if all aerobraking maneuvers possible get done. This means in ideal circumstances, not counting the reduced efficiency inside earths atmosphere, about 97.4% of the vehicles mass need to be fuel. AFAIK the best fuel fraction ever achieved for a fuel tank was 96% for the space shuttle ET. This means that even if your engine, heatshield, communications, etc. would weigh nothing, it would still be impossible with today's technology. And this isn't even accounting for cryogenic boil off and a lot of other problems with it.

The old Mercury-Atlas was practically an SSTO. It only dropped 2 engines but kept the rest of the rocket in one piece all the way to orbit.

On paper, the Titan II first stage with nothing on top of it is also said to have had enough dV to reach orbit. It was never flown this way because it would have needed the additional weight of a guidance system and a fairing, which probably would have made it too heavy, and also because the engines were not throttlable. Nowadays, a similar design to the these old rockets, with more efficient throttlable engines and modern avionics, could in theory make it as an SSTO, albeit with a very small payload.

The thing is, what's the point? SSTO alone achieves nothing and will always carry a much lower payload fraction than an MSTO launcher. If it's reusability you want, it can be done with or without SSTO, and all the gear and extra mass (structure, wings, TPS, landing gear, extra fuel...) required to return and land the vehicle only eats even more into the performance margin and the already insignificant payload fraction of an SSTO vehicle, making the whole exercice pointless.

Edited August 20, 2014 by Nibb31

[Red Iron Crown]

IMO, a lot of the SSTO proposals in the Science forum are based upon the overpoweredness of KSP SSTOs. When you have a tiny planet, awesomely efficient jet engines that work well at absurd altitudes and speeds, no reentry effects, and infinitely reliable and reusable parts, SSTOs become a whole lot more viable. They're fun, but not realistic and certainly not something to base a real life program on.

[R0cketC0der]

Posting from mobile, are we?

Stupid autocorrect. Well, I posted that from my iPad, so not exactly from my mobile.

Just want to point out that DerpenWolf's post is specifically not about dV from Earth surface. He wants to refuel in Earth orbit.

Ok, then I have misunderstood the OP. Reusable space tug seems a lot more possible with the possibility to use nuclear engines. That way, with no aerobraking(you probably wouldn't want to switch your heatshield in orbit), it would take about 14km/s delta-V. With a specific impulse of 950 seconds, you would only need around 80% of the mass of your vehicle to be fuel. If you also manage to refuel in low mars orbit, only half the delta-V would be necessary, so you would only need 55% of your vehicle to be fuel. You could also use ion engines which would give you a lot better payload fractions, but they also take longer to reach their target.

[KerikBalm]

Yea, a SSTO launcher is not neccessarily (and probably is not), a reusable launcher.

You could have a rocket with a ~25:1 Full:Empty mass ratio, and get it into orbit as a single stage - but its going to be so flimsy that it won't survive re-entry.

The space shuttle was mostly re-usable, I'm quite disappointed with how its economics worked out, I still think a similar concept could be done more economically.

Maybe ditch the winged vehicle idea in favor of standard capsules, heat shields, and parachutes.

Maybe add another, recoverable, stage, and ditch that single use, massive external tank.