Is it possible to docking while both vehicle are in suborbital trajetory?

[derega16]

I have really wild idea to push envelope of rocket's payload performance. Double simultaneously launch two rockets, first one put payload as much as it can liftoff even without sufficient dV to archive orbit, Second one don't have any payload but stretched upper stage tank or another upper stage. First one will deploy payload in suborbital, second one will catch-up with the payload and docking before reaching apogee and perform apogee burn for the payload. I know it is ridiculously risky and easier to just use a bigger rocket but is it possible to perform such maneuver in real life and KSP?

Edited May 12, 2020 by derega16

[linuxgurugamer]

KSP, Yes.  Real life, extremely improbable . You are talking about doing a separation and a rendezvous while in a sub orbital flight not having any time at all to spare for any mistakes in in accuracies etc

[Spacescifi]

5 minutes ago, derega16 said:

I have really wild idea to push envelope of rocket's payload performance. Double simultaneously launch two rockets, first one put payload as much as it can liftoff even without sufficient dV to archive orbit, Second one don't have any payload but stretched upper stage tank or another upper stage. First one will deploy payload in suborbital, second one will catch-up with the payload and docking before reaching apogee and perform apogee burn for the payload. I know it is ridiculously risky and easier to just use a bigger rocket but is it possible to perform such maneuver in real life and KSP?

Yes but the risk does not justify it.

I don't know about in KSP, but IRL a mere wind gust can be the difference between docking and colliding.

And it's not as if they are planes and get plenty of retries to dock.

Rockets stay in the air only a shot while before they reach space.

Margin for error is lower than normal launch.

That's why they don't do it.

Try it in KSP.

 

[RCgothic]

Technically yes, but practically no.

In order to effect an immediate rendezvous and docking the rockets would need to take off simultaneously from pads as close together as possible, or DV requirements rapidly become unmanageable.

Then you have to get the rendezvous right and complete the next burn before apogee on a very short orbit. Either that or you start getting very wasteful high-apogee suborbital orbits just to get enough time to dock.

Doing everything in such a rush and such proximity (and/or worse, inside a turbulent atmosphere) - is just insanely dangerous.

Edited May 12, 2020 by RCgothic

[derega16]

Just now, RCgothic said:

Technically yes, but practically no.

In order to effect an immediate rendezvous and docking the rockets would need to take off simultaneously from pads as close together as possible, or DV requirements rapidly become unmanageable.

Thenyou have to get the rendezvous right and complete the next burn before apogee on a very short orbit. Either that or you stay getting very wasteful high-apogee suborbital orbits just to get enough time to dock.

Doing everything in such a rush and such proximity (and/or worse, inside a turbulent atmosphere) - is just insanely dangerous.

About high orbit what if something like GEO transfer suborbital launch directly from the equator? It is most (kinda) reasonable reason to do something like this

[Nightside]

6 minutes ago, derega16 said:

About high orbit what if something like GEO transfer suborbital launch directly from the equator? It is most (kinda) reasonable reason to do something like this

What would the advantage be over just having different stages specialized for each environment? Many real rockets have 3-4 stages optimized for different parts of the launch, wouldn't that be more efficient?

What do think would happen if you had a "tugboat" already waiting to meet your spacecraft in GEO, and bring it up to orbital velocity?

[tater]

This has been discussed after a fashion in RL, only the docking is with a skyhook, not another LV (which would be stunningly difficult from a timing standpoint).

[sevenperforce]

This was proposed very seriously as a subset of the Black Horse orbital concept. Black Horse was a horizontal takeoff/landing rocketspaceplane that would have loaded up with oxidizer from a tanker before continuing to orbit. One of the alternate possibilities was that two Black Horse spaceplanes would launch onto a suborbital trajectory and mate, then transfer props from one to the other, and then the second would continue to orbit while the first would go back.

There's just not a lot of time for suborbital rendezvous.  

[Nuke]

probably not something anyone would plan for, but i kind of did it once in ksp to save a ship that didnt quite have the deltav to get into orbit. fortunately it was the hab stage for a jool mission and id already boosted the transfer stage, its orbit was close enough that i could plot a just in time intercept with the transfer stage. of course i had to send up a tanker to refuel it having burned a good portion of the deltav in the maneuver, but at least jeb and val didnt burn up. possible yes, but were in extreme situation territory.

Edited May 13, 2020 by Nuke

[kerbiloid]

We can launch them already docked. They would be stages.

[DDE]

46 minutes ago, kerbiloid said:

We can launch them already docked. They would be stages.

Then there's always this suborbital docking option:

[kerbiloid]

An orbital tugplane with a nuke with ISP*g > 8 km/s.

Hangs on orbit. Periodically dives into atmosphere, glides, collects liquid air as propellant, and returns to orbit.

A suborbital cargo plane jumps up to 80 km, releases payload. Returns to ground.
The orbital tugplane dives, catches the payload and returns to orbit. Releases the payload.

This works in circus, why shouldn't here.

Spoiler

 

[Codraroll]

I think you would be much better off with a launch vehicle that carried the payload safely to low Earth orbit, where it could sit for a while waiting for another spacecraft to be launched (at its own leisurely pace) to rendezvous, dock and transfer in the safety of the vacuum and stable(-ish) orbits, and then afterwards boost itself to whatever orbit it wants to go to. Doing it the KSP way, in other words.

[sevenperforce]

7 hours ago, kerbiloid said:

An orbital tugplane with a nuke with ISP*g > 8 km/s.

Hangs on orbit. Periodically dives into atmosphere, glides, collects liquid air as propellant, and returns to orbit.

A suborbital cargo plane jumps up to 80 km, releases payload. Returns to ground.
The orbital tugplane dives, catches the payload and returns to orbit. Releases the payload.

This works in circus, why shouldn't here.

  Hide contents

 

Hah!

This is a great idea right up until you do the math on how much drag is produced when you try to scoop the air. Drag is unavoidable here because you have to actually collect the air and take it back to orbit. 

Let's say notionally that we have a 5-tonne payload released at 100 km at 3 km/s (which is a hypersonic cargo plane but whatever). Let's say that the dry mass of our orbital nukeship is an impossible 1 tonne and it can push air at 815 s isp. In order to boost that 5 tonnes from 3 km/s to 8 km/s, it will need to burn 5.2 tonnes of propellant. Yet it's also going to need to match velocity in the first place, which means it needs to burn 5.4 tonnes to drop to that speed in the first place. So it needs to carry 10.6 tonnes of propellant per launch.

How does one dive and collect 10.6 tonnes of propellant? Here we have a problem. When you dive, the air you're encountering is not moving. Even with no parasitic drag whatsoever (i.e., it magically collects and liquifies 100% of the air molecules it encounters), your 1-tonne vehicle moving at 8 km/s will be moving at just 690 m/s after adding 10.6 tonnes of air. Burning to reach orbit again will leave you with only 3.66 tonnes of propellant.

So you make another pass.You collect less air, so now you're moving at 3.2 km/s after topping up your tanks, and your second burn leaves you with 5.4 tonnes of props. Another pass, and another, and another, and so on until your tanks are finally full. And all that, only if you can manage a mass fraction of 1:11 in a vehicle with a freaking nuclear engine...and one, I might add, with sufficient thrust to deliver 7.3 km/s in mere minutes.

 

[kerbiloid]

This was an idea from 1950s, to refuel the orbital spaceplanes from air...

[Starman4308]

On 5/13/2020 at 8:13 AM, sevenperforce said:

Hah!

This is a great idea right up until you do the math on how much drag is produced when you try to scoop the air. Drag is unavoidable here because you have to actually collect the air and take it back to orbit. 

Let's say notionally that we have a 5-tonne payload released at 100 km at 3 km/s (which is a hypersonic cargo plane but whatever). Let's say that the dry mass of our orbital nukeship is an impossible 1 tonne and it can push air at 815 s isp. In order to boost that 5 tonnes from 3 km/s to 8 km/s, it will need to burn 5.2 tonnes of propellant. Yet it's also going to need to match velocity in the first place, which means it needs to burn 5.4 tonnes to drop to that speed in the first place. So it needs to carry 10.6 tonnes of propellant per launch.

How does one dive and collect 10.6 tonnes of propellant? Here we have a problem. When you dive, the air you're encountering is not moving. Even with no parasitic drag whatsoever (i.e., it magically collects and liquifies 100% of the air molecules it encounters), your 1-tonne vehicle moving at 8 km/s will be moving at just 690 m/s after adding 10.6 tonnes of air. Burning to reach orbit again will leave you with only 3.66 tonnes of propellant.

So you make another pass.You collect less air, so now you're moving at 3.2 km/s after topping up your tanks, and your second burn leaves you with 5.4 tonnes of props. Another pass, and another, and another, and so on until your tanks are finally full. And all that, only if you can manage a mass fraction of 1:11 in a vehicle with a freaking nuclear engine...and one, I might add, with sufficient thrust to deliver 7.3 km/s in mere minutes.

 

For this to work: there is a hard constraint that exhaust velocity must at least match your velocity relative to atmosphere. It's actually a bit of a thorn in the side of any sci fi writer who wants spaceships refueling by dipping into the atmosphere of a gas giant: for that to provide net propellant, you need something like a fusion torch as your engine.

[Spacescifi]

18 minutes ago, Starman4308 said:

For this to work: there is a hard constraint that exhaust velocity must at least match your velocity relative to atmosphere. It's actually a bit of a thorn in the side of any sci fi writer who wants spaceships refueling by dipping into the atmosphere of a gas giant: for that to provide net propellant, you need something like a fusion torch as your engine.

 

A fusion torch itself is a thorn I believe.

How you gonna cool it? The more heatsinks you put on you lower overall thrust, unless you start feeding THAT as reaction mass, which means your dead after you exhaust them all.

Radiators need to huge, and in atmosphere that's a bad idea.

 

So honestly,I hate to say it, but if scifi writers wanba go hard with gas giant refueling, you need some kind project Orion/rocket SSTO hybrid that scoop the gas as it does reentry.

 

The orion pusher plate will provide tge thrust to retutn to space, while rockets will alliw for safe initial launch and landing.

[kerbiloid]

Huge scoops are the huge radiators.

Orion has nothing to do with gas.

Edited May 15, 2020 by kerbiloid

[Nothalogh]

On 5/12/2020 at 6:20 PM, linuxgurugamer said:

KSP, Yes.  Real life, extremely improbable . You are talking about doing a separation and a rendezvous while in a sub orbital flight not having any time at all to spare for any mistakes in in accuracies etc

Basically this scenario is the same as taking out a ballistic missile warhead with a hardkill interceptor, and illustrates why those ABM systems are so hard to perfect.

[magnemoe]

On 5/13/2020 at 12:25 AM, RCgothic said:

Technically yes, but practically no.

In order to effect an immediate rendezvous and docking the rockets would need to take off simultaneously from pads as close together as possible, or DV requirements rapidly become unmanageable.

Then you have to get the rendezvous right and complete the next burn before apogee on a very short orbit. Either that or you start getting very wasteful high-apogee suborbital orbits just to get enough time to dock.

Doing everything in such a rush and such proximity (and/or worse, inside a turbulent atmosphere) - is just insanely dangerous.

This, note that you can go mach 6 climb to 60 km deeply an second stage  and land downrange as in Falcon 9. Easier to just build an larger rocket. 
Yes a couple of KSP players has managed to grab something suborbital on Eve have an catch rocket dock with target and circulate. 
Couple of KSP community probably with lots of reloads and editing, couple of.
In real life this is harder than an ballistic anti satellite weapon as you also have to match trajectory and fast. 
 

[Guest]

9 hours ago, Nothalogh said:

Basically this scenario is the same as taking out a ballistic missile warhead with a hardkill interceptor, and illustrates why those ABM systems are so hard to perfect.

Not the same, worse. ABM only has to match position, for docking you need to match velocity, too. A hardkill interceptor doesn't really care how fast it hits, as long as it's above the "fast enough" threshold. 

[Nothalogh]

23 minutes ago, Dragon01 said:

A hardkill interceptor doesn't really care how fast it hits, as long as it's above the "fast enough" threshold. 

Much like docking in KSP