An SSTO as "God and Robert Heinlein intended".

[Matrix Aran]

I assume you mean reusable TSTOs since we already have TSTOs. SpaceX is working on reusable TSTOs. The Air Force is nearly there since they want to make the first stage reusable.

However, as is well known SSTO's have the characteristic that if refueled in LEO then they can fly to the Moon, land, lift off and fly back to Earth on that one single fuel load. This is not true of TSTO's where the upper stage might only get, say, a delta-v of 6,000 m/s.
So if one did have his own private, SSTO vehicle, then with propellant depots he would also have his own private lunar vehicle.
See discussion here:

SSTO's would have made possible Arthur C. Clarke's vision of 2001.
http://exoscientist.blogspot.com/2012/05/sstos-would-have-made-possible-arthur-c.html



Bob Clark

Begging your pardon, but I'm having trouble here. If you can refuel the SSTO and go to the moon, why not develop a TSTO that can be refueled in orbit and also go to the moon. Surely it would have the advantage of being a smaller mass being sent to the moon?

Which then begs another question, how would you get the fuel up there in the first place?

 

[RGClark]

Begging your pardon, but I'm having trouble here. If you can refuel the SSTO and go to the moon, why not develop a TSTO that can be refueled in orbit and also go to the moon. Surely it would have the advantage of being a smaller mass being sent to the moon?

Which then begs another question, how would you get the fuel up there in the first place?

Good question, which reminded me of another interesting fact. The explanation involves the concept of delta-v, which is the increase in velocity a rocket stage can impart. Note: a related but not quite the same use of the term is how much of a velocity change is required to complete a certain mission. For instance you'll see a phrase like the "delta-v to orbit is about 9,200 m/s."

Now for a two stage to orbit vehicle typically the largest delta-v is imparted by the upper stage at around 6,000 m/s, with the lower stage giving a smaller amount, around 3,000 m/s. Now, take a look at this diagram that give the delta-v requirements for getting to and from the Moon:

Delta-v budget.
Earth–Moon space — high thrust
http://en.wikipedia.org/wiki/Delta-v_budget#Earth.E2.80.93Moon_space_.E2.80.94_high_thrust

If you add up the delta-v required to get from LEO to the Moon and back again it's around 8,700 m/s. Note this is less than the delta-v needed to get to LEO.

However, it is true that the delta-v a stage can impart is dependent on how much payload it is carrying. So for instance a Centaur upper stage can be used on an Atlas V rocket or Delta IV rocket to carry a 10mT or 20mT payload to orbit. But it would not have enough delta-v if refueled in orbit to carry the same size payload to the Moon and back according to the amount of delta-v required for such a mission.

But if you wanted it to do this for a much smaller payload, it could. You can calculate that it could carry a bit more than 1 mT to the Moon and back if refueled in LEO. This would be useful for robotic missions to carry a robotic lander to the Moon to pick up samples to return to Earth. This would be useful for prospector missions. Note also since the delta-v to some near Earth asteroids is even less than that to the Moon, this could also be useful for prospector missions to some NEO's.


Bob Clark

 

[Matrix Aran]

Wouldn't this all be better achieved by a purpose built earth-moon "ferry", with cheap capsules to ferry crew back and forth to such a vessel? Without the mostly dead weight of a heat shield, and all the cacophony of other systems a SSTO would require?

I have to say, it seems like trying to use an SSTO for such a mission seems like an effort to take a square peg and hammer it into a small round hole.

P.S. I forgot to mention, you still haven't answered my question on how you would get the fuel to refuel any ship up into orbit in the first place.

 

[Cras]

How safe do you see refueling in orbit? or any "wild" environment. NASA made it seem like such a delicate process when tanking the Space Shuttle, I always wondered how feasible it would be to fuel up space craft out in space, considering both the environment, and the fact that the crew has to be the ones doing it. Fuel type has something to do with it as well I would imagine.

 

[Hlynkacg]

How safe do you see refueling in orbit? or any "wild" environment. NASA made it seem like such a delicate process when tanking the Space Shuttle, I always wondered how feasible it would be to fuel up space craft out in space, considering both the environment, and the fact that the crew has to be the ones doing it. Fuel type has something to do with it as well I would imagine.

Q: How do you handle an explosive device?

A: Carefullly.

It's less to do with the delicacy of the procedure itself and more to do with the fact that you're transporting large amounts of highly volatile substances. Refuelling in orbit may actually be safer in the sense that there is less chance of a stray spark or cigarette-butt blowing the whole pad to kingdom come and that a space-suited astronaut has little to fear from toxic fumes.

 

[T.Neo]

If you want space technology to mature, you will have to refuel in space sometime. Best to bite the bullet and make the effort to develop the technology rather than live in fear of the effort and never have the advantage of the final product.

Also: it is entirely possible to create a fully reusable, robust cislunar (for example) architecture using a TSTO and a dedicated in-space transportation unit or tug. Such a tug could be a modified second stage- it would have none of the superfluous hardware that a Moon-landing SSTO would have to possess and would be far less technologically demanding while being far more practical.

 

[Cras]

Q: How do you handle an explosive device?

A: Carefullly.

It's less to do with the delicacy of the procedure itself and more to do with the fact that you're transporting large amounts of highly volatile substances. Refuelling in orbit may actually be safer in the sense that there is less chance of a stray spark or cigarette-butt blowing the whole pad to kingdom come and that a space-suited astronaut has little to fear from toxic fumes.

If you want space technology to mature, you will have to refuel in space sometime. Best to bite the bullet and make the effort to develop the technology rather than live in fear of the effort and never have the advantage of the final product.

Quite right indeed. EVAs seemed to be quite the difficult task to master, but once it was, NASA was able to do some masterful things, such as built a space station, and walk on the moon. Refueling in space seems to be a very useful, if not vital knowledge to gain for future space flight, I just wonder how easy it will be to master.

 

[Matrix Aran]

I agree with you all, on orbit refueling is quite necessary to move forward, and the dangers don't seem too difficult to overcome. I'm just curious about how anyone plans on getting the fuel up to orbit in the first place. Well curious, and slightly concerned that someone is then going to suggest using an SSTO for fuel transport.

 

[RGClark]

Wouldn't this all be better achieved by a purpose built earth-moon "ferry", with cheap capsules to ferry crew back and forth to such a vessel? Without the mostly dead weight of a heat shield, and all the cacophony of other systems a SSTO would require?
I have to say, it seems like trying to use an SSTO for such a mission seems like an effort to take a square peg and hammer it into a small round hole.
P.S. I forgot to mention, you still haven't answered my question on how you would get the fuel to refuel any ship up into orbit in the first place.

The advantage is one of having your own, personal launch vehicle, that can also take you to the Moon with orbital refueling. I do also like the idea of having ferry vehicles though.
For getting the fuel to orbit, there have been proposals of using low cost and low reliability rockets to get consumables such as fuel, water, food, etc. to orbit. While these proposed rockets would have a higher rate of failure they would be launched at high rates which would help to lower the cost. So the lost cargo would be easily made up for by the high launch rates.
This of course would require a market for large amounts of payload to be sent to orbit, which I argue would be the case with large numbers of privately owned SSTO's.
Other methods to get large amounts of propellant to orbit at low cost might be railguns or cannon launch. These can be done now for small payloads. You would run them continually to get the large amounts of fuel to orbit.
It is notable that both of these could be done much more easily if done from the Moon because of the lower delta-V required to achieve orbit and because you don't have the dense atmosphere to contend with.
I'll write about these in an upcoming blog post.


Bob Clark

---------- Post added at 03:34 AM ---------- Previous post was at 02:36 AM ----------

How safe do you see refueling in orbit? or any "wild" environment. NASA made it seem like such a delicate process when tanking the Space Shuttle, I always wondered how feasible it would be to fuel up space craft out in space, considering both the environment, and the fact that the crew has to be the ones doing it. Fuel type has something to do with it as well I would imagine.

True, but note that the ISS is refueled on a regular basis by the Progress cargo craft, though with non-cryogenic propellants.
NASA has also done studies that show large BEO missions can be accomplished much more cheaply if propellant depots are in place.


Bob Clark

 

[Urwumpe]

The main problems during fueling of a rocket are cryogen fuels and corrosive fuels. The first are the most annoying, since they require careful thermal conditioning of the tanks if you don't want to destroy the tanks by thermal stress.

Corrosive fuels are pretty nasty, if you don't keep things and especially contact plates absolutely clean. Valves are especially vulnerable.

the tanking procedure of the ISS for example, is still taking many hours of careful operations: And that just for maximal 1700 kg propellant, which is only corrosive.

 

[Matrix Aran]

Personaly owned SSTO's? I can hardly afoard to fill up my Citroen V6's tank days. I'd hate to imagine the bill from Grumman for filling up the tank on my SSTO!

And not to nitpick here, but railguns or cannon aren't exempt from the law of conservation of energy. You would need quite a large powerplant supplying them, wouldn't you?

One other thing, but I thought that the latest railgun the Navy was working on only had a range of about 370 Km, the projectile was hardly spacecraft sized and if I recall correctly the projectile was photographed with what looked like either a fire or plasma trail, I'm not sure which. Either way it didn't quite look like a safe way to launch fuel, but I digress.

Urwumpe makes a very good point that while refueling in orbit is possible, its a very delicate operation still, which again makes me wonder just how much I'd enjoy spending a tedious day in orbit refueling my personal SSTO.

Is the dream of us all one day owning our own spacecraft the only real benefit to SSTO's or am I missing something?

 

[T.Neo]

The idea of personally owned spacecraft follows the model of aircraft more than automobiles, I think. Owning your own RLV would be somewhat like owning a private jet- only for those who are wealthy and the highly dedicated.

SSTO design isn't beneficial for a privately-owned vehicle- for reasons that have been explained ad nauseam in this thread. The propulsion and structural requirements are more demanding than for a TSTO vehicle (for example), increasing production and flight costs.

 

[RGClark]

...
SSTO design isn't beneficial for a privately-owned vehicle- for reasons that have been explained ad nauseam in this thread. The propulsion and structural requirements are more demanding than for a TSTO vehicle (for example), increasing production and flight costs.

No they aren't. They are the same as already produced vehicles. SpaceX deserves credit for producing a lightweight stage in the Falcon 9 first stage, but then they saddled it with engines no more efficient than those produced in the very earliest days of spaceflight.
Orbital Sciences deserves credit for using the highly efficient NK-33 engine on their Taurus II, renamed the Antares, rocket, but then they saddled it with stages no more weight efficient than those from the very earliest days of spaceflight.
To produce the SSTO you just do what's obvious: use both the most efficient engines and the most efficient stages at the same time.


Bob Clark

---------- Post added at 01:43 AM ---------- Previous post was at 01:01 AM ----------

...
And not to nitpick here, but railguns or cannon aren't exempt from the law of conservation of energy. You would need quite a large powerplant supplying them, wouldn't you?
One other thing, but I thought that the latest railgun the Navy was working on only had a range of about 370 Km, the projectile was hardly spacecraft sized and if I recall correctly the projectile was photographed with what looked like either a fire or plasma trail, I'm not sure which. Either way it didn't quite look like a safe way to launch fuel, but I digress.
....
Is the dream of us all one day owning our own spacecraft the only real benefit to SSTO's or am I missing something?

Actually the energy costs for getting to orbit are surprisingly low, less than a dollar a kilogram:

http://home.earthlink.net/~kstengel226/astro/cost2orbit.html

The scientists and engineers who have studied cannon launch and railgun launch are confident propellant and small size satellites can be launched safely using them:

http://yarchive.net/space/exotic/gun_launch.html

Having personal vehicles to orbit is a pretty significant benefit in regards to making spaceflight routine.


Bob Clark

 

[Matrix Aran]

Having personal vehicles to orbit is a pretty significant benefit in regards to making spaceflight routine.


Bob Clark

Doesn't space flight have to become routine before people will trust it enough to own personal vehicles to orbit? This is starting to sound like the story about the chicken and egg.

 

[Notebook]

From RGClark #313 above.

The scientists and engineers who have studied cannon launch and railgun launch are confident propellant and small size satellites can be launched safely using them

Don't forget the slingatron:

http://www.slingatron.com/spacelaunch.htm

Though it may make you dizzy at launch...

N.

 

[T.Neo]

No they aren't. They are the same as already produced vehicles. SpaceX deserves credit for producing a lightweight stage in the Falcon 9 first stage, but then they saddled it with engines no more efficient than those produced in the very earliest days of spaceflight.
Orbital Sciences deserves credit for using the highly efficient NK-33 engine on their Taurus II, renamed the Antares, rocket, but then they saddled it with stages no more weight efficient than those from the very earliest days of spaceflight.
To produce the SSTO you just do what's obvious: use both the most efficient engines and the most efficient stages at the same time.

You've made the very poor assumption that every space launch vehicle, its engines/tankage/etc, is equal in cost. This is wrong.

You've argued the physics ad infinitum. Noone is actually doubting much of what you say there (mostly just the technical absurdity how you present the ease of marrying together different LV components).

The main issue here is the economics- and in specific, the economics of an SSTO compared to a TSTO (since you have to justify the concept you are supporting compared to its competitors). And this analysis in the full sense is far more in-depth than any of the math you've done here.

But from a basic viewpoint, reality is in your way: the more advanced technology that you require is obviously going to cost more than the less advanced technology that a TSTO requires. This is what has been argued by everyone else ad infinitum.

 

[Urwumpe]

More important question: How much better is a SSTO with zero staging systems (which can be complex) compared to a TSTO with one staging system. Even by physics alone, it is hard to justify, things only get interesting if you include logistics. And even transporting a single stage rocket to 17 km altitude by plane is a TSTO, though an ineffective one.

 

[RGClark]

From RGClark #313 above.



Don't forget the slingatron:

http://www.slingatron.com/spacelaunch.htm

Though it may make you dizzy at launch...

N.

Thanks for the link. I had heard of the Slingatron but I had thought the projectiles were accelerated by EM fields. So I thought it was in a similar class to the railgun or coilgun. But apparently they are accelerated mechanically, like someone twirling around a bob at the end of a string, which is a different type of launch process.


Bob Clark

---------- Post added at 09:31 AM ---------- Previous post was at 09:27 AM ----------

Doesn't space flight have to become routine before people will trust it enough to own personal vehicles to orbit? This is starting to sound like the story about the chicken and egg.

That's not how it happened in the aircraft industry, which is another reason why such vehicles need to be privately developed aside from the fact the development costs can by cut by 90%(!)

Bob Clark

 

[Urwumpe]

That's not how it happened in the aircraft industry, which is another reason why such vehicles need to be privately developed aside from the fact the development costs can by cut by 90%(!)

If you don't do any research at all, you can reduce your R&D costs by more than 90%. But generally a really poor choice since you can only fight by the profit margins then. A reduction in R&D costs is no innovation or achievement to be proud of. If the R&D costs in the actual product per flight or flight article is reduced, it is a small achievement, but generally, it is not important. The total cost of ownership is more important.

Also, the aircraft industry had always been driven by military and companies, but private research had a strong impact for the first years until the idea was getting mature. If you would apply the same logic to SSTOs, they would already be an oddity of the early days of rocketry, while TSTOs will dominate the market - because the market is dominated by TSTOs.

 

[Notebook]

Thanks for the link. I had heard of the Slingatron but I had thought the projectiles were accelerated by EM fields. So I thought it was in a similar class to the railgun or coilgun. But apparently they are accelerated mechanically, like someone twirling around a bob at the end of a string, which is a different type of launch process.

well.
N.