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Old 04-17-2019, 02:00 PM
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tbzep tbzep is offline
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Default Antares Launch

Just looking at info for today's Antares launch.
As a short background, Orbital ATK's Antares 1st stage is from the Russian company that makes the Zenit, and it uses a pair of Energomash designed RD-181's.
2nd stage is a solid Castor 30 series, IIRC.

That's where it's interesting. Falcon 9 has a quick staging process, as did the Saturns, etc. The Antares has a 43 second coast phase where it will drop interstages, fairings, etc. before the Castor lights. That reminds me of a lot of sounding rocket flight profiles.

I wonder if it has anything to do with the hot rod RD-181's. They are way more than the Antares needs and have been used at a partial throttle setting to keep from over stressing the airframe. Was the flight profile the same with the old AJ26 (Russian NK-33)?
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Old 04-17-2019, 07:11 PM
BARGeezer BARGeezer is offline
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Listening to the audio, it sounds like everything was nominal.
https://www.youtube.com/watch?v=LNCJmOKH-n0


Interesting contrast between the reactions of the flight control rooms of Northrop Grumman and Space X when successful milestones are announced.
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Old 04-17-2019, 08:52 PM
frognbuff frognbuff is offline
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Quote:
Originally Posted by tbzep
Just looking at info for today's Antares launch.
As a short background, Orbital ATK's Antares 1st stage is from the Russian company that makes the Zenit, and it uses a pair of Energomash designed RD-181's.
2nd stage is a solid Castor 30 series, IIRC.

That's where it's interesting. Falcon 9 has a quick staging process, as did the Saturns, etc. The Antares has a 43 second coast phase where it will drop interstages, fairings, etc. before the Castor lights. That reminds me of a lot of sounding rocket flight profiles.

I wonder if it has anything to do with the hot rod RD-181's. They are way more than the Antares needs and have been used at a partial throttle setting to keep from over stressing the airframe. Was the flight profile the same with the old AJ26 (Russian NK-33)?


Orbital/Orbital-ATK/NGIS uses the coast period for trajectory shaping on their all-solid propellant vehicles. See, for example, the Pegasus flight profile info here: https://infogalactic.com/info/Pegasus_(rocket)

So, I'm guessing this has more to do with the solid-propellant second-stage on Antares than anything to do with the throttleable RD-181s. All-liquid vehicles do their trajectory shaping via longer burns and/or multiple burns, which solids don't offer.

Hopefully Matt Steele will weigh in and set us all straight!
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Old 04-17-2019, 09:55 PM
ManofSteele ManofSteele is offline
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The profile of Antares is largely based on Orbital's legacy scheme for orbital vehicles, that is correct.

Because you can't throttle down the solids at MaxQ for real-time load relief, the tendency is loft the birds higher, then "turn right and go fast" to get to orbital velocity.

The RD181s are powerful, so you will hear at the end of the burn that they gradually throttle them down to minimize loads on the vehicle prior to staging (which is the tricky part).

The flight computer records the the vehicle flight state at burnout, then calculates in real time the optimal time for second stage ignition to place the payload in the proper orbit. Not as necessary with the Antares first stage, that can be shut off by command, but a very nice way of accounting for all the variables for a multi stage solid rocket motor launch vehicle.

Congratulations to the NGIS Antares team and all the support folks at MARS that made the launch a very smooth success. I liked that they named this Cygnus for Roger Chaffee.

Matt
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Old 04-18-2019, 06:19 AM
frognbuff frognbuff is offline
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Thanks Matt! That makes perfect sense!

Kudos to the NGIS team for the fairing mods which allowed late cargo loading. That is a very cool solution. I can't think of a single vehicle today that allows you to detach the entire nose section like that. Access doors? Sure, everybody does that. But a bolt-on section including the split line? That is truly unique!

Link: https://spaceflightnow.com/2019/04/...us-supply-ship/
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