Skyhiker-Skyhitch towed SSTO

[IsaacKuo]

The Skyhiker-Skyhitch SSTO system uses a small spaceplane that is towed/pushed most of the way up. The components are:

A) Two small Skyhiker SSTO spaceplanes. The L-SSTO launches from Earth to orbit. The R-SSTO returns from orbit to Earth. Skyhiker is similar to X-37B upscaled by 2X.

B) Two jet tow planes. One tows L-SSTO to altitude. The other tows R-SSTO back to home base. To minimize development costs, these are existing jets with a tow cable added.

C) One large Skyhitch tow rocket. This brakes from orbit and returns to orbit with L-SSTO. To minimize development costs, this is shaped like the Space Shuttle Orbiter. Internally it's a flying fuel tank that uses internal pressure for structural strength and open cycle cooling of the TPS to minimize the mass that must be reboosted back to orbit.

This system assumes CO/LOX resupply in space. See my Deimos dust potato gun rocket for LMO atmospheric scooping.

Skyhiker's launch procedure is:

1) L-SSTO is hitched to tow jet on runway.

2) Jet launches and tows L-SSTO to high altitude. The rocket is optimized for high altitude/vacuum.

3) L-SSTO boosts to 2km/s as R-SSTO brakes to meet it. Mass ratio about 2:1.

10T Payload
10T L-SSTO dry mass
20T Fuel

4) R-SSTO pushes L-SSTO from 2km/s up to 4km/s as Skyhitch brakes to meet it. Mass ratio about 2:1. Note that R-SSTO's cargo tank is filled with fuel.

10T Payload
10T L-SSTO dry mass
10T R-SSTO dry mass
30T Fuel

5) Skyhitch pushes L-SSTO from 4km/s up to 7.8km/s. Mass ratio about 4:1.

10T Payload
10T L-SSTO dry mass
20T Skyhitch dry mass
120T Fuel

6) R-SSTO glides to second jet for towing back toward home base. It lands horizontally.

In a sense, Skyhitch replaces a giant first stage. But since Skyhitch never returns to the ground, it doesn't need landing gear and it doesn't need to be integrated with an upper stage on the ground. This avoids costs associated with a reusable TSTO. Instead, ground operations are airplane-like (very cheap!).

Note that the pushing operations take place in vacuum after L-SSTO has emptied its fuel tanks. This eliminates aerodynamic forces and mitigates pushing ring force. It's quite a contrast with a traditional multi-stage rocket, where the lower stages must accelerate the fully fueled upper stages through the lower atmosphere.

Because Skyhitch externally looks like the STS Orbiter, it might be initially launched by SLS, bolted onto the side. That would look...amusing.

[wuzetian]

The Skyhiker-Skyhitch SSTO system uses a small spaceplane that is towed/pushed most of the way up. The components are:

A) Two small Skyhiker SSTO spaceplanes. The L-SSTO launches from Earth to orbit. The R-SSTO returns from orbit to Earth. Skyhiker is similar to X-37B upscaled by 2X.

B) Two jet tow planes. One tows L-SSTO to altitude. The other tows R-SSTO back to home base. To minimize development costs, these are existing jets with a tow cable added.

C) One large Skyhitch tow rocket. This brakes from orbit and returns to orbit with L-SSTO. To minimize development costs, this is shaped like the Space Shuttle Orbiter. Internally it's a flying fuel tank that uses internal pressure for structural strength and open cycle cooling of the TPS to minimize the mass that must be reboosted back to orbit.

This system assumes CO/LOX resupply in space. See my Deimos dust potato gun rocket for LMO atmospheric scooping.

Skyhiker's launch procedure is:

1) L-SSTO is hitched to tow jet on runway.

2) Jet launches and tows L-SSTO to high altitude. The rocket is optimized for high altitude/vacuum.

3) L-SSTO boosts to 2km/s as R-SSTO brakes to meet it. Mass ratio about 2:1.

10T Payload
10T L-SSTO dry mass
20T Fuel

4) R-SSTO pushes L-SSTO from 2km/s up to 4km/s as Skyhitch brakes to meet it. Mass ratio about 2:1. Note that R-SSTO's cargo tank is filled with fuel.

10T Payload
10T L-SSTO dry mass
10T R-SSTO dry mass
30T Fuel

5) Skyhitch pushes L-SSTO from 4km/s up to 7.8km/s. Mass ratio about 4:1.

10T Payload
10T L-SSTO dry mass
20T Skyhitch dry mass
120T Fuel

6) R-SSTO glides to second jet for towing back toward home base. It lands horizontally.

In a sense, Skyhitch replaces a giant first stage. But since Skyhitch never returns to the ground, it doesn't need landing gear and it doesn't need to be integrated with an upper stage on the ground. This avoids costs associated with a reusable TSTO. Instead, ground operations are airplane-like (very cheap!).

Note that the pushing operations take place in vacuum after L-SSTO has emptied its fuel tanks. This eliminates aerodynamic forces and mitigates pushing ring force. It's quite a contrast with a traditional multi-stage rocket, where the lower stages must accelerate the fully fueled upper stages through the lower atmosphere.

Because Skyhitch externally looks like the STS Orbiter, it might be initially launched by SLS, bolted onto the side. That would look...amusing.

So many throws and catches in supersonic speeds ... Ha ha

[IsaacKuo]

Eh, there are only two encounters at supersonic speeds, and they can both use near vacuum aerodynamic control at the start of the pushing maneuver. We regularly perform aerial refueling which uses the same basic technique. In both cases, the incoming pusher vehicle has an extreme reserve of speed to perform turning and braking maneuvers to meet the client vehicle. In the first case, the client vehicle is also under active rocket power up until right before they meet.

There is no case where anything is "thrown" toward some target position. It's all controlled flight.

The third encounter is between the gliding return SSTO and the second tow jet. There is no reason this needs to take place at supersonic speeds. The returning SSTO can be gliding at, say, 200mph, by the time it meets the tow jet. There's no hurry on this one because it starts off at a high altitude and it just doesn't matter if they lose a lot of altitude while hooking up the tow line.

[Jim]

Skyhitch tow rocket is a non starter.  Braking all the mass of propellant and then reboosting is not viable.  It would take a large surface area to brake the mass.

Also, it is not feasible to brake to a specific velocity and altitude.  They are interrelated.  There still will be heating at 2 km/s.  Propulsion will be require.

The whole concept is unworkable.

[Almurray1958]

Not quite sure that something with 2 tow planes and a tow rocket can be called a SINGLE stage to orbit. The  mission profile is complex

[Jim]

Because Skyhitch externally looks like the STS Orbiter, it might be initially launched by SLS, bolted onto the side. That would look...amusing.

Not doable.  Would require redesign of SLS core and VAB

[Jim]

The other tows R-SSTO back to home base.

Why?  Just let it land itself.

[IsaacKuo]

Well, we typically don't call strap on boosters another stage, nor do we call the payload spacecraft another stage even if it generally has its own thrusters to reach the desired orbit. It's kind of fuzzy.

I call it an SSTO to emphasize that the lack of stage integration on the ground. In a sense, hitching the tow cable is "integrating" the tow jet and the SSTO, but this is practically nothing in time and effort compared to the strap on boosters we ignore.

The Space Shuttle Orbiter has demonstrated that it is indeed possible to brake from orbit, while performing S-turns that provide a large amount of cross-range capability and which reaches a specific narrow target slot and altitude (otherwise, it would crash somewhere other than the landing runway). There is some development required to replace the heavy STS's TPS tiles with an open cycle cooled system, but I think that may be the best option since it reduces the amount of dry mass that must be accelerated back from 4km/s to orbit.

[Jim]

The Space Shuttle Orbiter has demonstrated that it is indeed possible to brake from orbit, while performing S-turns that provide a large amount of cross-range capability and which reaches a specific narrow target slot and altitude (otherwise, it would crash somewhere other than the landing runway). There is some development required to replace the heavy STS's TPS tiles with an open cycle cooled system, but I think that may be the best option since it reduces the amount of dry mass that must be accelerated back from 4km/s to orbit.

Not filled with the amount of propellant (4km/s) that you propose.
The shuttle TPS is not "heavy".  It would be lighter than open cooled system

Landing is not the same as targeting a specific altitude and velocity

[hkultala]

Well, we typically don't call strap on boosters another stage

Who is "we"?

On the world most used launcher family, the "boosters" are called stage 1, the "core" is called stage 2.

And, boosters are universally considered to be a a stage, even when they are not called "stage 1". Booster separation is considered as a staging event.


You call your system "SSTO" because you just think than "SSTO is cool", and you want pto propose something cool, even though on the way you lose then SSTO part.

[IsaacKuo]

The other tows R-SSTO back to home base.

Why?  Just let it land itself.

Depending on the specifics, such as launching to the ISS orbit from KSC, it would be over the Atlantic Ocean heading east. While it might use parachutes and floats to land on the ocean, you've got to deal with ocean water damage (especially to the engines) and a time consuming recovery process.

[Jim]

The other tows R-SSTO back to home base.

Why?  Just let it land itself.

Depending on the specifics, such as launching to the ISS orbit from KSC, it would be over the Atlantic Ocean heading east. While it might use parachutes and floats to land on the ocean, you've got to deal with ocean water damage (especially to the engines) and a time consuming recovery process.

depending on tow is not viable.  Even current mid air refueling have failed hookups.

[Archibald]

You'd better have to mixed propulsion (jet-rocket) suborbital space planes refueling in suborbital flight at the top of a parabola. Only a single rendezvous and propellant transfer.

[IsaacKuo]

You'd better have to mixed propulsion (jet-rocket) suborbital space planes refueling in suborbital flight at the top of a parabola. Only a single rendezvous and propellant transfer.

The dry mass of a jet engine would eat away at the payload, and would add greatly to development costs (in contrast to being towed by an already existing jet). Fuel transfer could, in principle, make things more efficient. Originally, I conceived of the SSTO as refueling in mid-boost.

The launch SSTO could take off much lighter, and it would top off at altitude from a tanker. The returning SSTO could refuel the launch SSTO at 2km/s and the R-SSTO's dry mass wouldn't need to be re-accelerated up to 4km/s.

But carbon monoxide/lox are cryogenic fuels. You'd have to develop a dual feed cryogenic aerial refueling system rather than using an off-the-shelf tanker jet. And such an aerial refueling system would be heavier than a simple tow hook and a pushing ring.

(I'm not sure whether a pushing ring would be better or a tow cable. Here, I illustrate a pushing ring at the rear of the SSTO. But I do like the idea of using a tow cable for all steps.)

[ppb]

You'd better have to mixed propulsion (jet-rocket) suborbital space planes refueling in suborbital flight at the top of a parabola. Only a single rendezvous and propellant transfer.

The dry mass of a jet engine would eat away at the payload, and would add greatly to development costs (in contrast to being towed by an already existing jet). Fuel transfer could, in principle, make things more efficient. Originally, I conceived of the SSTO as refueling in mid-boost.

The launch SSTO could take off much lighter, and it would top off at altitude from a tanker. The returning SSTO could refuel the launch SSTO at 2km/s and the R-SSTO's dry mass wouldn't need to be re-accelerated up to 4km/s.

But carbon monoxide/lox are cryogenic fuels. You'd have to develop a dual feed cryogenic aerial refueling system rather than using an off-the-shelf tanker jet. And such an aerial refueling system would be heavier than a simple tow hook and a pushing ring.

(I'm not sure whether a pushing ring would be better or a tow cable. Here, I illustrate a pushing ring at the rear of the SSTO. But I do like the idea of using a tow cable for all steps.)

Hey you got Jim to critique your idea! Lucky you. Listen to what he says.

[Lars-J]

There's at least 4 stages for this ... "SSTO". 

Google "skyhook structure" for a far more practical way to do what you are trying to accomplish. This is what I assumed you were going to describe based on the thread title.

[IsaacKuo]

There's at least 4 stages for this ... "SSTO". 

Google "skyhook structure" for a far more practical way to do what you are trying to accomplish. This is what I assumed you were going to describe based on the thread title.

Besides being a hazard to LEO use, a tether is extremely inflexible in terms of what orbits and launch sites it can service. It practically can only support one inclination and one launch site.

This Skyhitch concept can support multiple launch sites and can service a different orbit each time thanks to the turning capability of the winged space planes while braking. Bleeding speed down to 2km/s or 4km/s allows turning by a large angle and large cross range capability. Practically speaking, any launch site and any orbit may be serviced.

Also, it's harder to latch onto a skyhook because the window is very brief. An 2km/s arc could start with a 600m/s upward velocity, offering two minutes to hook up before starting to renter thicker air. And even then, gliding together offers more time to hook up. Depending on the mass of the payload, there will be a variable extra margin of delta-v to make up for gliding drag.

[Jim]

This Skyhitch concept can support multiple launch sites and can service a different orbit each time thanks to the turning capability of the winged space planes while braking. Bleeding speed down to 2km/s or 4km/s allows turning by a large angle and large cross range capability.

Wrong.  Not feasible in this concept.    And there is no way to sustain level controlled flight to allow the hookup.  The "braking" vehicle is going to be in a descending flight path.  And still in a entry attitude.

[Jim]

Also, it's harder to latch onto a skyhook because the window is very brief. An 2km/s arc could start with a 600m/s upward velocity, offering two minutes to hook up before starting to renter thicker air. And even then, gliding together offers more time to hook up. Depending on the mass of the payload, there will be a variable extra margin of delta-v to make up for gliding drag.

Wrong.  it will be just as hard to latch up.  It is not "gliding".  It is descending at a high rate.

There is no way two vehicle can rendezvous at 2km/sec is too fast to be "flying" and too slow to be orbiting..
At what altitude do you propose this to happen?

[Jim]

This thread has some of the same nonsense.  It was shown that it is not feasible to work for some of the same reasons.

https://forum.nasaspaceflight.com/index.php?topic=41207.0

[IsaacKuo]

I've finally figured out a way to use cable towing for all steps, eliminating the nose push tail ring.

The key is to use a half-loop cable rather than a line and drogue. The ends of the cable are attached to the wings, which keeps the cable clear of rocket exhaust.

The Skyhiker has a nose hook that looks like a navy jet's tail hook. But instead of being mounted underneath the tail, this nose hook is mounted above the nose.

To use, the hook is rotated up vertically so it sticks above the Skyhiker. A high angle of attack helps the hook poke well above the rudders. As the half-loop of the tow cable passes by slowly, the hook is inserted into the loop's gap and catches the bend at the rear.

[Jim]

I've finally figured out a way to use cable towing for all steps, eliminating the nose push tail ring.

So what is protecting the cable from aeroheating at 2km/sec?

If you are not going to answer questions posed to you or ignore points that show the infeasibility of the concept, I am going to ask for this thread to be locked.

[IsaacKuo]

I don't really have the inclination to argue with someone who doesn't think it's possible to pitch upward with an aircraft, braking while changing the heading to 15 degree upward (thus entering an upward ballistic trajectory).

Mid-air refueling is a thing that actually happens. Controlled gliding from orbit to a specific altitude and position actually happens. What's the point of arguing with someone who denies that these things can be done?

[IsaacKuo]

So what is protecting the cable from aeroheating at 2km/sec?

The thinness of the atmosphere at the altitudes used, along with choice of cable material to let it handle the heating that it does encounter. My guess is that some type of steel may be the best choice, since it can be pretty durable under a wide range of conditions.

[hkultala]

I don't really have the inclination to argue with someone who doesn't think it's possible to pitch upward with an aircraft, braking while changing the heading to 15 degree upward (thus entering an upward ballistic trajectory).

Mid-air refueling is a thing that actually happens.

Supersonic or hypersonic mid-air-refueling does not happen. Refueling is currently only performed on subsonic speeds, AND it's only performed when both aircrafts are under thrust.

Controlled gliding from orbit to a specific altitude and position actually happens.

.. with huge wings, when this specific altitude is 0 so that there is LOTS OF TIME to do the manouvering.

Trying to rendeznous something running at hypersonic speed is totally different thing than landing into stationary runway.

What's the point of arguing with someone who denies that these things can be done?

You are messing up completely different things. Much easier things are done and you are using this as a claim that much harder things can be done.

[Jim]

1.  I don't really have the inclination to argue with someone who doesn't think it's possible to pitch upward with an aircraft, braking while changing the heading to a 15 degree upward (thus entering an upward ballistic trajectory).

2.  Controlled gliding from orbit to a specific altitude and position actually happens.

The issue isn't me proving anything.  It's your concept and you have made many unsupported assumptions, that basically show a lack of understanding the environment

1.  We aren't talking about aircraft or "gliding".  This is a entry vehicle going at 2km/sec.  It is going hypersonic.   It would have to be at 50km altitude or more due to heating.  It can't "pull up".  Increasing lift is going to cause temperature to go too high (shuttle flew at 40 deg AOA, any lower and it would over heat).   The shuttle never climbed during entry

2.  No.  The shuttle did not glide to specific altitude, position and time.  It landed at a specific point but that is not the same.   The shuttle controlled energy and it flew a trajectory that was some what variable.

[hkultala]

So what is protecting the cable from aeroheating at 2km/sec?

The thinness of the atmosphere at the altitudes used, along with choice of cable material to let it handle the heating that it does encounter. My guess is that some type of steel may be the best choice, since it can be pretty durable under a wide range of conditions.

What is your "altitude used" ?

Let me quess: You have not decided it.

SR-71 was flying at much lower speeds, at very high altitudes, and it needed titanium  for critical parts of the airframe to survive the heat from the drag.

[Jim]

The thinness of the atmosphere at the altitudes used, along with choice of cable material to let it handle the heating that it does encounter. My guess is that some type of steel may be the best choice, since it can be pretty durable under a wide range of conditions.

Can't have both a thin atmosphere to reduce heating yet be thick enough to support flight.   
There isn't going to be a cable that can survive the heating.

This is where you don't understand "flight'.  Unpowered flight (gliding) does not occur over 33km or so.  The shuttle is falling.

[Archibald]

This thread has some of the same nonsense.  It was shown that it is not feasible to work for some of the same reasons.

https://forum.nasaspaceflight.com/index.php?topic=41207.0

This thread also had a lot of trolling by a certain member (mansol )

[IsaacKuo]

So what is protecting the cable from aeroheating at 2km/sec?

The thinness of the atmosphere at the altitudes used, along with choice of cable material to let it handle the heating that it does encounter. My guess is that some type of steel may be the best choice, since it can be pretty durable under a wide range of conditions.

What is your "altitude used" ?

Let me quess: You have not decided it.

SR-71 was flying at much lower speeds, at very high altitudes, and it needed titanium  for critical parts of the airframe to survive the heat from the drag.

I don't know the exact altitude appropriate, but it would be something in the range of X-15 flight. The SR-71 was designed for sustained level flight, not short term ballistic flight like the X-15. You use lift for maneuvering while braking, not for level flight while sustaining speed.

In this regime, the Space Shuttle Orbiter has a lift:drag glide ratio of around 1:1. This sounds horrible, but it's actually just fine. You are trading speed for turning, which is a familiar concept for anyone familiar with air combat maneuvering - turning bleeds speed like crazy. But here's the point--it can be done and it has been demonstrated in real life. Hypersonic reentry research vehicles have done hairpin turns. That doesn't imply doing a hairpin turn while maintaining constant speed. No, a hairpin turn bleeds away a lot of speed.

But we want to bleed away a lot of speed - and quickly! The more quickly the speed is bled, the shorter the exposure to heating. Most of this heating will be experienced by the wings, since they have the largest area.

So, we do one or more S turns to bleed away speed and maneuver to the desired position and velocity to meet L-SSTO. At the end of this, we do a final upward turn to direct our velocity vector on a 15 degree upward angle. This puts us on a ballistic path into thinner air, going upward at around 600m/s. That's around one scale height every ten seconds. So drag is halved every ten seconds. So I can't really say exactly how much drag and heating the cable will suffer when it's deployed, but it can be halved by waiting another ten seconds.

Roughly speaking, the total drag and heating will be about twice that of the first ten seconds (1+1/2+1/4+1/8+... = 2). This is just a rough approximation, since gravity will halt upward velocity in a minute (there's another minute before falling to the original altitude). But it gives an idea of the order of magnitude.

For the second encounter, the initial upward velocity is much greater. At 4km/s, a final upward turn of 15 degrees implies an upward velocity of around 1200m/s. That's about a scale height every five seconds, and it will continue upward for two minutes (with another two minutes before falling back to the original altitude).

[IsaacKuo]

I don't really have the inclination to argue with someone who doesn't think it's possible to pitch upward with an aircraft, braking while changing the heading to 15 degree upward (thus entering an upward ballistic trajectory).

Mid-air refueling is a thing that actually happens.

Supersonic or hypersonic mid-air-refueling does not happen. Refueling is currently only performed on subsonic speeds, AND it's only performed when both aircrafts are under thrust.

There are particular practical reasons why refueling is only done under those conditions, but they are not relevant to the control problem of aligning the two vehicles with great precision.

Controlled gliding from orbit to a specific altitude and position actually happens.

.. with huge wings, when this specific altitude is 0 so that there is LOTS OF TIME to do the manouvering.

The spacecraft considered here have huge wings. And not all reentry vehicles are designed to take a long time to reach the ground. While it massively increases the TPS requirements, military ballistic missiles are designed to reach the target quickly to better penetrate enemy defenses. Maneuvering is also used to help penetrate enemy defenses.

Trying to rendeznous something running at hypersonic speed is totally different thing than landing into stationary runway.

As far as the control system is concerned, it really isn't that different. You've got particular coordinates in space-time that you're trying to reach. In this case, the virtual runway coordinates are moving like a very fast aircraft carrier, at the desired rendezvous. It's fundamentally like trying to land on a runway with an extremely fast headwind.

You are messing up completely different things. Much easier things are done and you are using this as a claim that much harder things can be done.

I'm not the one who claimed that mid-air towing for the final vehicle is impossible because sometimes mid-air refueling hookups don't work. That's for the easiest hookup by far - the one where the returning R-SSTO is hooking up with the F15 for final towing back toward home base. In this much slower regime, the glide ratio is much better and the forward speed much lower, so the descent rate is not so bad. The F15 jet can fly ahead of the R-SSTO all the way down without breaking a sweat. It's not like those helicopter attempts to capture a parachuting payload where it's hard or impossible to get more than one attempt. This jet can fly parallel to this glider the whole way down.

[hkultala]

It's fundamentally like trying to land on a runway with an extremely fast headwind.

Nobody is/has been landing an (orbital) glider into very fast headwind.

Shuttle had tight weather requirements for landing.

[hkultala]

I don't really have the inclination to argue with someone who doesn't think it's possible to pitch upward with an aircraft, braking while changing the heading to 15 degree upward (thus entering an upward ballistic trajectory).

Mid-air refueling is a thing that actually happens.

Supersonic or hypersonic mid-air-refueling does not happen. Refueling is currently only performed on subsonic speeds, AND it's only performed when both aircrafts are under thrust.

There are particular practical reasons why refueling is only done under those conditions, but they are not relevant to the control problem of aligning the two vehicles with great precision.

Yes they are. Things like shock wave of the first aircraft affects the control of the second aircraft

[Archibald]

This thread has some of the same nonsense.  It was shown that it is not feasible to work for some of the same reasons.

https://forum.nasaspaceflight.com/index.php?topic=41207.0

Once you desorbit (below 7.2 km/s) , there is no (easy) way back into orbit, even for a stage crammed with propellant.

I often wonder if the NRO ever tried brief desorbit / re-orbit of their Agena-based Key Holes, for better resolution ? How low could a satellite "dive" before kamikazing into the atmosphere ?

[Jim]

1.  I don't know the exact altitude appropriate, but it would be something in the range of X-15 flight. The SR-71 was designed for sustained level flight, not short term ballistic flight like the X-15.

2.  You use lift for maneuvering while braking, not for level flight while sustaining speed.

3.  In this regime, the Space Shuttle Orbiter has a lift:drag glide ratio of around 1:1. This sounds horrible, but it's actually just fine. You are trading speed for turning, which is a familiar concept for anyone familiar with air combat maneuvering - turning bleeds speed like crazy. But here's the point--it can be done and it has been demonstrated in real life. Hypersonic reentry research vehicles have done hairpin turns. That doesn't imply doing a hairpin turn while maintaining constant speed. No, a hairpin turn bleeds away a lot of speed.

4.  But we want to bleed away a lot of speed - and quickly! The more quickly the speed is bled, the shorter the exposure to heating. Most of this heating will be experienced by the wings, since they have the largest area.

5.  So, we do one or more S turns to bleed away speed and maneuver to the desired position and velocity to meet L-SSTO. At the end of this, we do a final upward turn to direct our velocity vector on a 15 degree upward angle

This post is bereft of reality

1. Non plausible.   at X-15 highest altitudes, reaction control was needed.  At the its lowest altitudes, 2km/sec would have too much heating.

2. Wrong.  No, lift was used for braking.  The shuttle used reaction control  for maneuvering.  In fact, some thrusters were used down to 50kft. 

3.  Proof please.  a 180 degree turn does not equate to "hairpin"

4 And the intensity of the heating is greater.  What TPS is going to be used?

5.  wrong.  Climbing is not possible.

[Jim]

I don't really have the inclination to argue with someone who doesn't think it's possible to pitch upward with an aircraft, braking while changing the heading to 15 degree upward (thus entering an upward ballistic trajectory).

Mid-air refueling is a thing that actually happens.

Supersonic or hypersonic mid-air-refueling does not happen. Refueling is currently only performed on subsonic speeds, AND it's only performed when both aircrafts are under thrust.

There are particular practical reasons why refueling is only done under those conditions, but they are not relevant to the control problem of aligning the two vehicles with great precision.

Yes they are. Things like shock wave of the first aircraft affects the control of the second aircraft

And since this is supposedly done at 2km/sec, the shock wave is huge and there is a ionization sheath.  There will be no visibility.

[Archibald]

There were talk in the aerospaceplane days of hypersonic refueling to be tested by a pair of X-15s. the idea was rightly discarded before flight testing began... while X-15 suborbital flights were rather begnin, hypersonic records took a toll on the structure, with the scramjet mockup standing on the way of the hypersonic flow.

[Vultur]

I have to say this seems overly complex to be economical.

1. Non plausible.   at X-15 highest altitudes, reaction control was needed.  At the its lowest altitudes, 2km/sec would have too much heating.

Sure, but the max altitude flights of X-15 were not the max speed flights. The speed record of X-15 (which was around 2 km/s, 4520 mph) was set at "only" ~31km.

[CameronD]

There were talk in the aerospaceplane days of hypersonic refueling to be tested by a pair of X-15s. the idea was rightly discarded before flight testing began... while X-15 suborbital flights were rather begnin, hypersonic records took a toll on the structure, with the scramjet mockup standing on the way of the hypersonic flow.

{emphasis mine} I think Michael J. Adams (and others in ground control) would disagree with you.

https://en.wikipedia.org/wiki/X-15_Flight_3-65-97

 

[Katana]

There were talk in the aerospaceplane days of hypersonic refueling to be tested by a pair of X-15s. the idea was rightly discarded before flight testing began... while X-15 suborbital flights were rather begnin, hypersonic records took a toll on the structure, with the scramjet mockup standing on the way of the hypersonic flow.

{emphasis mine} I think Michael J. Adams (and others in ground control) would disagree with you.

https://en.wikipedia.org/wiki/X-15_Flight_3-65-97

And the SR71 / D21 air launch collision