How do you handle variations in launches with a solid second stage?

Question

Watching the Antares launch for Orb-1 mission of Cygnus, I was thinking about the booster.

First stage is built in Ukraine by the company that makes the Zenit. They use the NK-33 engine, (Called an AJ-26 in the US) built in the 1960's (!! Yes, engines could be older than most of the people working on the project) for the Soviet N-1 Moon launch vehicle.

Second stage is stranger, to me, if you can believe it! They use ATK Castor solid rockets.

Thus the question, if the first stage has a 'burp' for some reason and say first stage thrust is low, or high, or 'wrong', and you fire your second stage solid, how do you correct?

When the SpaceX Falcon 9 'burped' an engine on a flight, they throttled up the other 8 engines and basically burned a little bit longer.

The second stage had some level of throttle control and timing control to adjust for that to keep the mission on track. (The secondary payload for Orbcomm that was lost, was not deployed, because of NASA rules on orbits that approach the ISS, where they are super picky and strict).

What would Orbital do, with a solid second stage in that case? You get two options. On, and burned out. Do you have to use an upper (third or payload based) stage to correct any variations?

Keep in mind that SpaceX's Falcon 9 has 9 engines, and so it can afford to lose one (at certain point during flight - it can't lose one right on startup, for example) and keep going. Antares has only two engines on the bottom, so I think that if even 1 was lost at any point in the flight it would be mission-ending. — Nickolai, Jan 09 '14 at 19:31
@user2544357 No argument. However a 'burp' in an engine, an underperformance, and overperformance, a different performance is really what I was referring too. Not a full engine loss, in this specific example. — geoffc, Jan 09 '14 at 19:39

PearsonArtPhoto · Accepted Answer · 2014-01-09T18:23:29.753

9

A solid rocket can stop early, and typically in a situation where they rely on it, they will have extra fuel, and just cut off the rocket early. This is very commonly done for missile systems, which have to be very flexible, and be able to fire with little time, and near other people. In addition, they can correct for other wrongness by moving the thrust nozzle for thrust vector control.

The thrust is stopped early by blowing out the engine. Usually there are port covers near the top that reduce the pressure, reducing the effectiveness of the thrust. Also, you can blow out the engine, or a number of alternatives to stop the engine immediately, the key is to lose the containment of the pressure, and the fuel will suddenly leave the rocket at minimal thrust.

If they can achieve orbit, they can use the payload to make up for some slight differences as well.

edited Jan 09 '14 at 18:23

answered Jan 09 '14 at 18:16

PearsonArtPhoto

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Have you seen that Castor 30 has a thrust vectoring nozzle? – geoffc Jan 09 '14 at 18:25
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@geoffc - there are explosively opened ports for counterthrust. – Deer Hunter Jan 09 '14 at 18:28
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@DeerHunter That must not be a very pleasant experience for the payload, I would imagine. What kind of load does that engender? I guess it has to be designed to handle the end of thrust, normally, I wonder how much more violent this would be? – geoffc Jan 09 '14 at 18:34
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@geoffc - please have a look at Minotaur I launch guide. For lighter payloads, the load is stated to be between 6.7 G and 12.1 G. – Deer Hunter Jan 10 '14 at 00:03

How do you handle variations in launches with a solid second stage?

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