AntARES-I launch vehicle

[rklaehn]

Hi all,

One thing that is a bit strange about the Antares launch vehicle is that the first stage is a relatively high Isp liquid engine, whereas the second stage is a low Isp but high thrust solid rocket motor. Ideally it should be the other way round. Low Isp/high thrust for the first stage, and high Isp for the second stage.

Given that ATK and Orbital now already work together on launch vehicles, can anybody estimate what payload you could expect by doing an ARES-I/Liberty style launch vehicle? Using an Antares first stage as a second stage on top of a five segment ATK RSRM.

I made a crude estimate from the data on www.spacelaunchreport.com, and I get about 15000kg to LEO. See calculation below.

For antares as a second stage, you could probably get away with just one AJ-26/NK-33 engine on the Antares stage. This could be optimized for vacuum operation, giving it an Isp in the range of the NK-43 engine (346 s).

The diameter of the RSRM (3.71m) is similar to the diameter of the Antares first stage (3.9m), so you would have a more favorable aerodynamic configuration compared to the ARES-I and Liberty proposals. Also, since both companies are american there would be less trouble with ITAR.

Moderators: I am not sure if this is the right section for this topic. Feel free to place it somewhere more appropriate. Maybe there should be a dedicated "armchair launch vehicles" section...

Simple spreadsheet based on spacelaunchreport data
https://docs.google.com/spreadsheet/pub?key=0AqQNEy5_BA9idDdKVFYybDRMUk9GNUlWMThLaURUdVE&output=html

[Kaputnik]

Would an NK-43 be a viable option for the upper stage?

[hkultala]

Would an NK-43 be a viable option for the upper stage?

No, because it lacks thrust vectoring needed for control, would need another engine for control. AJ26-60 has 2-way thrust vectoring but it still lacks roll control.

[Lar]

Would an NK-43 be a viable option for the upper stage?

No, because it lacks thrust vectoring needed for control, would need another engine for control. AJ26-60 has 2-way thrust vectoring but it still lacks roll control.

Verniers for roll control?

[deltaV]

How about using two Aerojetized NK-43s and stretching the second stage (propellant tanks) a bit?

[rklaehn]

How about using two Aerojetized NK-43s and stretching the second stage (propellant tanks) a bit?

I am not sure if two NK-43 with the larger vacuum-optimized nozzles fit under the stage. A small dedicated roll control system should be possible. That is what they did for the first stage of ARES-X, right?

[rklaehn]

I updated the spreadsheet with a column "optimistic assumptions". In those I have subtracted the weight of one engine from the upper (ex-Antares) stage and assumed the Isp 346s of a NK-43 instead of the vacuum Isp 331s of the NK-33 / AJ-26.

The payload grows to a respectable 19500kg.

https://docs.google.com/spreadsheet/pub?key=0AqQNEy5_BA9idDdKVFYybDRMUk9GNUlWMThLaURUdVE&output=html

[deltaV]

How about using two Aerojetized NK-43s and stretching the second stage (propellant tanks) a bit?

I am not sure if two NK-43 with the larger vacuum-optimized nozzles fit under the stage.

Good point, the NK-33s barely fit as is. Never mind.

[aero]

Does anyone know why the launch profile includes a 95 second coast before SII ignition? Was it just a way to allow SI to do a full length burn, then let gravity draw the energy down until it was right for SII to place the payload into orbit, since SII can't be shut down?

[Lar]

Does anyone know why the launch profile includes a 95 second coast before SII ignition? Was it just a way to allow SI to do a full length burn, then let gravity draw the energy down until it was right for SII to place the payload into orbit, since SII can't be shut down?

This was answered on another thread (this thread is for a variant launch vehicle) but IIRC, it's so that the end of the burn is at the right place/time, rather than 'drawing energy down'

Although I suppose you could argue those are different ways of saying the same thing.

[deltaV]

Liquid rockets can restart half an orbit after orbital insertion to raise perigee. Solid rockets cannot restart (without another stage) so they need to get to the desired orbit at burnout. This requires that burnout altitude be at least perigee altitude. It takes time to climb, hence the coasting. The two stages are sort of like the two burns in a Hoffman transfer. (Caveat: IANARS and I'm not 100% sure of this. But it makes sense.)