SSTO (Single Stage to Orbit) Idea

[martinc]

Hi, guessed this was right forum for this, I would be really interested to know if this could work

Basically instead of launching a crewed vehicle into a standard low orbit you just aim for a sub-orbital trajectory with a 10 minute or so window at say 130 to 150 miles apogee.
Meanwhile an already orbiting space tug slows down to match and latches onto the craft boosting it into a standard LEO orbit
The negatives I can see already would be double hit on the tug to slow down (or perhaps drop out of a higher orbit where the speed would already match) then boost again
On the other hand the tug would only need to be a pure single function vehicle that could itself be re-fuelled from Progress style resupply missions and be kept permanently in orbit for this task
And of course the crewed vehicle would have dramatically lower mass and only a single stage
It's beyond me to work out the efficiencies to this approach

Probably there's already concepts for this I just haven't heard about yet
PS Originally I got the idea thinking about ways of launching from a floating Venus base where a SSTO would be very desirable indeed

Any thoughts appreciated
Martin

[Jim]

Hi, guessed this was right forum for this, I would be really interested to know if this could work

Basically instead of launching a crewed vehicle into a standard low orbit you just aim for a sub-orbital trajectory with a 10 minute or so window at say 130 to 150 miles apogee.
Meanwhile an already orbiting space tug slows down to match and latches onto the craft boosting it into a standard LEO orbit

The velocity matching is not feasible.  You are talking 1000's of meters/sec difference.
Here is the quickest illustration that I can do using real numbers. 

Geostationary orbit (35,786 km) orbit speed is 3.1 km/s
Molniya orbit (500 to 39,900 km) which is like a suborbital lob, at its apogee, the speed is 1.5 km/s

[Solman]

 The orbiting craft could in principle use aerobraking in a series of stages perhaps to slow down and meet a vehicle launched from the ground outside the atmosphere. That still leaves the challenges of grabbing the payload within the short window and of course how to refuel the orbital vehicle among others.
 Some time ago I proposed something I called the 'Space Basd Space Transportation System" and which Asteroza calls a "reverse bomber" IIUC, that woulld use NEO derived propellant for refueling in LEO and would use small rugged vehicles( in my version) based on kinetic kill vehicle type tech launched from one or both vehicles to connect a tow cable between them. The much larger orbital or tow vehicle would be serviced and refueuled at a facility on orbit.
In my version the tow connection is nade between an air breathing hypersonic vehicle and the tow vehicle so the window was shorter as the hypersonic vehicle zoom climbs to 50 km or so - hence the need for the connection vehicles.
Assuming NEO mining's development; it seemed to me that there might be a large surplus of material looking for a buyer at least at first, and this idea certainly requires a lot of propellant.

Yes I lnow there are a lot of issues and signifigant hand waving required but maybe it will inspire someone - or not .

[whitelancer64]

For spacecraft rendezvous to work, the two must not only be in the same place at the same time, but also traveling in the same orbit and at the same speed. The tug would have to change its orbit to match that of the target spacecraft, requiring whatever fuel is necessary to do so, and then the fuel to change the orbit of both to the target orbit. It's much more efficient for the spacecraft to already have the fuel or another stage already on it to do the maneuvering to the target orbit, which is what is already done.

This is why anyone claiming that rendezvousing with a comet is a "free ride to the outer solar system" is wrong. It's also why the problem of cleaning up orbital debris is so difficult.

[Jim]

The orbiting craft could in principle use aerobraking in a series of stages perhaps to slow down and meet a vehicle launched from the ground outside the atmosphere.

Using aerobraking in stages makes it impossible. 

The moment the orbiting vehicle (chaser) brakes and has the same velocity as the target vehicle, it is now in the same suborbital trajectory and needs to accelerate within minutes to stay in orbit.

So "aerobraking in a series of stages perhaps to slow down" is going to take the chaser out of orbit before it even able to meet the target vehicle.

A specific altitude, location and velocity (speed and direction) defines a specific orbit.   Any other orbits that pass through that specific altitude and location are going to be at a different velocity.  So the only way* to bring to vehicles together at specific altitude and location and not crash means they will have to be at velocity and therefore, they are in the same orbit.

* tethers are outside of this discussion, since that means external forces are present

[Jim]

This is a concept that many people fail to grasp

A specific altitude, location and velocity (speed and direction) defines a specific orbit.   Any other orbits that pass through that specific altitude and location are going to be at a different velocity.

So two orbits that share a common point means objects in those orbits will have different velocities at that point.

The movie "Mission to Mars" has a great example of failing to grasp this concept.

The part is when the MTV loses its engines before braking into Mars orbit and the crew decide to do an EVA from the MTV to the REMO in mars orbit.  In reality, the velocity differences would be in the km/sec range.

[martinc]

Jim, for sure the velocity change would be needed to this to work,

What I need to do, if i'm going to carry on with the concept is to work out approximately how much of a sub-orbital velocity a SSTO could reach and how heavy it's gonna be. Then I could work how how many tons would be needed to boost it up into LEO and how many tons the tug would then need to slow down and need in total
these numbers would then make or break the idea
I have a feeling unless it was under 10 tons of prop, with a tug weight of a couple tons, it's just not gonna work
On the other hand Mir was deorbited with a Progress carrying about 2 tons so maybe there's hope yet

[Jim]

What I need to do, if i'm going to carry on with the concept is to work out approximately how much of a sub-orbital velocity a SSTO could reach and how heavy it's gonna be. Then I could work how how many tons would be needed to boost it up into LEO and how many tons the tug would then need to slow down and need in total
these numbers would then make or break the idea

No, you did not read my post. 

For this to work, the target vehicle is going to have to brake hard (large thrusters) to slow and dock then accelerate hard to stay in orbit.   

 You are not saving propellant but in fact using more and ignoring the time it takes to do the actual rendezvous and docking.  Just to show you that you are not saving anything.  Look at a case where both vehicles have the same mass.  So the target vehicle brakes, docks and then reaccelerates.  You realize that the amount of propellant the target vehicle uses to reaccelerate would be the same amount to bring the suborbital chaser into orbit?  The amount of propellant to brake was wasted or most of it (it is way more than what is need to deorbit either craft)

On the other hand Mir was deorbited with a Progress carrying about 2 tons so maybe there's hope yet

No not a valid example, it is doing the opposite of what you want.  The Progress burn was a long one and it did not make the MIR suborbital.  It just lowered a part of the orbit into the atmosphere, where the air did the rest of the work.

[martinc]

ok Jim let's leave it at that until i can come back with figure's that work, we're all on the same side here. of course i read your post which just said 'it can't be done', well then its on me to show different but simply stating saying that on an internet forum you can't seriously expect me to accept it without a bit more proof can you?  you may have that proof but i don't so allow space for those that do not, but don't expect them to just believe your words as if they were carven on stone tablets

[Solman]

The orbiting craft could in principle use aerobraking in a series of stages perhaps to slow down and meet a vehicle launched from the ground outside the atmosphere.

Using aerobraking in stages makes it impossible. 

The moment the orbiting vehicle (chaser) brakes and has the same velocity as the target vehicle, it is now in the same suborbital trajectory and needs to accelerate within minutes to stay in orbit.

So "aerobraking in a series of stages perhaps to slow down" is going to take the chaser out of orbit before it even able to meet the target vehicle.

A specific altitude, location and velocity (speed and direction) defines a specific orbit.   Any other orbits that pass through that specific altitude and location are going to be at a different velocity.  So the only way* to bring to vehicles together at specific altitude and location and not crash means they will have to be at velocity and therefore, they are in the same orbit.

* tethers are outside of this discussion, since that means external forces are present

 I think you missunderstand the concept. The orbital vehicle slows down to a suborbital velocity using one or more entries into the upper atmosphere. It could be a waverider or winged. The vehicle to be towed to orbit executes a steep cimb or is launched on such a trajectory, and rendevous with the decelerated tow vehicle and tow line connected. The tow vehicle drags a payload capsule or even entire vehicle to orbit.
 Obviously the tow vehicle needs to be very large felative to the payload since the payload would have only a fraction of orbital velocity when picked up. Hydrolox probably for propellant as well. Any directional changes required for the tow vehicle to pick up the payload are by aerodynamics.

[Jim]

 I think you missunderstand the concept. The orbital vehicle slows down to a suborbital velocity using one or more entries into the upper atmosphere. It could be a waverider or winged. The vehicle to be towed to orbit executes a steep cimb or is launched on such a trajectory, and rendevous with the decelerated tow vehicle and tow line connected. The tow vehicle drags a payload capsule or even entire vehicle to orbit.
 Obviously the tow vehicle needs to be very large felative to the payload since the payload would have only a fraction of orbital velocity when picked up. Hydrolox probably for propellant as well. Any directional changes required for the tow vehicle to pick up the payload are by aerodynamics.

No, you don't understand orbital mechanics or aerobraking.  Aerobraking only provides a small decrease (few ft/sec) each orbital pass.  Even with wings and TPS, it is going to be more like reentry.  Going suborbital means 1000's of ft/sec below orbital velocity. 

Again, it is just not workable.  There is no "towing"   The speeds have to be equal when the towline is connected.

Aerodynamic control is not effective enough for this.  If you are talking about "flying" to connect the towline, that would be deep into the atmosphere.

This is really fiction.

[Jim]

ok Jim let's leave it at that until i can come back with figure's that work, we're all on the same side here. of course i read your post which just said 'it can't be done', well then its on me to show different but simply stating saying that on an internet forum you can't seriously expect me to accept it without a bit more proof can you?  you may have that proof but i don't so allow space for those that do not, but don't expect them to just believe your words as if they were carven on stone tablets

I gave you the proof.

[Solman]

 I think you missunderstand the concept. The orbital vehicle slows down to a suborbital velocity using one or more entries into the upper atmosphere. It could be a waverider or winged. The vehicle to be towed to orbit executes a steep cimb or is launched on such a trajectory, and rendevous with the decelerated tow vehicle and tow line connected. The tow vehicle drags a payload capsule or even entire vehicle to orbit.
 Obviously the tow vehicle needs to be very large felative to the payload since the payload would have only a fraction of orbital velocity when picked up. Hydrolox probably for propellant as well. Any directional changes required for the tow vehicle to pick up the payload are by aerodynamics.

No, you don't understand orbital mechanics or aerobraking.  Aerobraking only provides a small decrease (few ft/sec) each orbital pass.  Even with wings and TPS, it is going to be more like reentry.  Going suborbital means 1000's of ft/sec below orbital velocity. 

Again, it is just not workable.  There is no "towing"   The speeds have to be equal when the towline is connected.

Aerodynamic control is not effective enough for this.  If you are talking about "flying" to connect the towline, that would be deep into the atmosphere.

This is really fiction.

Jim you know better. It can skip off the atmosphere and slow down like a stone skipping on water for instance.
What gave me the idea originally was the German skip bomber concept.
Also as it slows down it can go into the stratosphere as needed.

[AlesH]

I completely agree with Jim. It is impossible to reasonably "move energy" of orbital "tug" to suborbital "craft". For any suborbital trajectory is always more effective to accelerate "craft" only (itself), than trying to accelerate an additional "tug" (moreover weight). It should be obvious even intuitively.

[Solman]

I completely agree with Jim. It is impossible to reasonably "move energy" of orbital "tug" to suborbital "craft". For any suborbital trajectory is always more effective to accelerate "craft" only (itself), than trying to accelerate an additional "tug" (moreover weight). It should be obvious even intuitively.

I guess I'm just not a very good explained.
The tug starts off in orbit fully fueled by NEO derived hydrology. It then decelerates in a series of skip maneuvers  until it reaches the velocity of the launched vehicle and matches it's trajectory briefly.
At this point it is still fully fueled more or less (boiloff).
The two craft are joined by cable while outside the atmosphere and the tug takes it to orbit.
Remember the idea was to sell propellant from NEO's.
No magic needed.

[Toast]

I completely agree with Jim. It is impossible to reasonably "move energy" of orbital "tug" to suborbital "craft". For any suborbital trajectory is always more effective to accelerate "craft" only (itself), than trying to accelerate an additional "tug" (moreover weight). It should be obvious even intuitively.

I guess I'm just not a very good explained.
The tug starts off in orbit fully fueled by NEO derived hydrology. It then decelerates in a series of skip maneuvers  until it reaches the velocity of the launched vehicle and matches it's trajectory briefly.
At this point it is still fully fueled more or less (boiloff).
The two craft are joined by cable while outside the atmosphere and the tug takes it to orbit.
Remember the idea was to sell propellant from NEO's.
No magic needed.

You didn't listen to Jim at all. If it slows to the velocity of the launched vehicle AND matches its position AND matches its trajectory, then they are (by definition) in the same orbit (or in this case, suborbital trajectory). Which means there is no benefit. There is no way to keep the orbital tug in orbit while rendezvousing with a craft on a suborbital trajectory. If it goes from an orbital trajectory to a suborbital trajectory and accelerates (with the added mass of the suborbital craft) back to orbital velocity, then you are using significantly more propellant to do so, and it would be far more efficient to launch it all at once and avoid the orbital tug launch, refueling, and rendezvous altogether.

EDIT: Grammar.

[hkultala]

I completely agree with Jim. It is impossible to reasonably "move energy" of orbital "tug" to suborbital "craft". For any suborbital trajectory is always more effective to accelerate "craft" only (itself), than trying to accelerate an additional "tug" (moreover weight). It should be obvious even intuitively.

I guess I'm just not a very good explained.
The tug starts off in orbit fully fueled by NEO derived hydrology. It then decelerates in a series of skip maneuvers  until it reaches the velocity of the launched vehicle and matches it's trajectory briefly.

There are no such "skip manouvers" that makes this possible.

It burns in atmosphere and/or drops to ground (has an orbit that goes THROUGH earth) before it can reach so low velocity that it can match with the other craft (which is not SSTO, please try to understand what SSTO means), unless the other craft is going at about >95% of orbital velocity, and then this another craft and extra complexity makes absolutely no sense at all for the final 5%.

[spacenut]

There is only two ways I see a SSTO.  One is that it would have to be very large, like Bono's Rombus type vehicle.  Two a vehicle like Skylon.  Venture Star might have worked had they used off the shelf technology and/or limited payload capacity. 

SpaceX and Blue Origin are trying for TSTO with the possibility of a reusable second stage.  Smaller vehicles for the payload delivered. 

[Solman]

I completely agree with Jim. It is impossible to reasonably "move energy" of orbital "tug" to suborbital "craft". For any suborbital trajectory is always more effective to accelerate "craft" only (itself), than trying to accelerate an additional "tug" (moreover weight). It should be obvious even intuitively.

I guess I'm just not a very good explained.
The tug starts off in orbit fully fueled by NEO derived hydrology. It then decelerates in a series of skip maneuvers  until it reaches the velocity of the launched vehicle and matches it's trajectory briefly.
At this point it is still fully fueled more or less (boiloff).
The two craft are joined by cable while outside the atmosphere and the tug takes it to orbit.
Remember the idea was to sell propellant from NEO's.
No magic needed.

You didn't listen to Jim at all. If it slows to the velocity of the launched vehicle AND matches its position AND matches its trajectory, then they are (by definition) in the same orbit (or in this case, suborbital trajectory). Which means there is no benefit. There is no way to keep the orbital tug in orbit while rendezvousing with a craft on a suborbital trajectory. If it goes from an orbital trajectory to a suborbital trajectory and accelerates (with the added mass of the suborbital craft) back to orbital velocity, then you are using significantly more propellant to do so, and it would be far more efficient to launch it all at once and avoid the orbital tug launch, refueling, and rendezvous altogether.

EDIT: Grammar.

Sigh
1. Yes the tug does go from orbit to a suborbital trajctory.
2. A payload container as I said is preferred, but the whole vehicle is possible not necessary.
3. At the moment of connection it is different from a second stage with payload only in that the payload is trailing behind on a cable and this second stage has wings, thermal protection, and the rendezvous system. This does add some mass but
4. The underlying assumption is that NEO derived propellant is available and cheap so the advantage lies in the fact that a first stage can launch as payload the mass that otherwise would include a second stage and its propellant. Also you don't have to buy a second stage.

[Solman]

I completely agree with Jim. It is impossible to reasonably "move energy" of orbital "tug" to suborbital "craft". For any suborbital trajectory is always more effective to accelerate "craft" only (itself), than trying to accelerate an additional "tug" (moreover weight). It should be obvious even intuitively.

I guess I'm just not a very good explained.
The tug starts off in orbit fully fueled by NEO derived hydrology. It then decelerates in a series of skip maneuvers  until it reaches the velocity of the launched vehicle and matches it's trajectory briefly.

There are no such "skip manouvers" that makes this possible.

It burns in atmosphere and/or drops to ground (has an orbit that goes THROUGH earth) before it can reach so low velocity that it can match with the other craft (which is not SSTO, please try to understand what SSTO means), unless the other craft is going at about >95% of orbital velocity, and then this another craft and extra complexity makes absolutely no sense at all for the final 5%.

Look up the skip bomber or America bomber concept by Eugen Sanger.