Author Topic: Orbital's Antares Discussion Thread (to Hotfire Test and debut flight)  (Read 31104 times)

Offline Silmfeanor

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The second stage is inside the fairing, isn't it? How could it possibly ignite before fairing separation?

Comga means during 1st stage flight

Offline Kabloona

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Just noticed this from the AONE-Mission Overview PDF.
The fairing is jettisoned BEFORE second stage ignition while the stack is in freefall. 
Why is this supperior to jettison while accelerating?  There is excess capacity being trimmed as gravity losses in the adjustable duration of the long coast.  Why not start accelerating earlier and jettison a few seconds later while the acceration can help the fairing halves depart?

It may be because of the way the interstage is designed. If you look closely at that graphic, you can see both halves of the PLF and the interstage ring falling away from S2. So S1 separates below the interstage, and then the PLF and interstage separate from S2.

If that is in fact how it works, then the interstage can't be separated during S2 firing because of the possibility it could contact the nozzle. So the interstage and PLF must be jettisoned first.

Plus, there's no point wasting deltaV, no matter how little, on the PLF that you're jettisoning. It's designed to jettison all by itself without needing any deltaV from S2. Only reason to delay PLF jettison is atmospherics, and apparently it'll be high enough before S2 igntion anyway.

The cutaway in this brochure shows more clearly how the interstage works.

http://www.orbital.com/NewsInfo/Publications/Antares_Brochure.pdf

Could be wrong but that's my hypothesis.
« Last Edit: 04/08/2013 11:38 PM by Kabloona »

Online Comga

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The second stage is inside the fairing, isn't it? How could it possibly ignite before fairing separation?

Comga means during 1st stage flight

Thanks but no, I just forgot about that little interstage, and how it is what holds the fairing.  I was going to ask about that but didn't to keep the post short.

That's the answer.  The second stage would have to drag that interstage to keep the fairing with it.

It is an intersting set of system choices.  Many are the polar opposites of "the other CRS provider."
What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

Offline Kabloona

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The second stage is inside the fairing, isn't it? How could it possibly ignite before fairing separation?

Comga means during 1st stage flight

It is an intersting set of system choices.  Many are the polar opposites of "the other CRS provider."

The difference from F9 being that the Castor 30 is a smaller diameter than S1, and thus you need the conical adapter ring, as opposed to F9's simpler load path through S2.

So in this case it's the dimensions of the Castor 30 that drives the interstage design and staging sequence.

Offline Lurker Steve

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I was wondering exactly how large of a payload Antares could deliver to GTO. My thinking was that Orbital could be a "single-source" supplier that eventually they would be a one-stop shop where Intelsat or SES would purchase a SAT with X amount of transpoders, and Orbital could put that into the correct orbit using Antares.

It looks like a SAT the size of SES-8 is about 3.5 mT, so that's probably out of their range at the moment.

Offline Jim

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I was wondering exactly how large of a payload Antares could deliver to GTO. My thinking was that Orbital could be a "single-source" supplier

Not usually done.  See Boeing and LM spacecraft
« Last Edit: 04/12/2013 09:22 PM by Jim »

Offline baldusi

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I was wondering exactly how large of a payload Antares could deliver to GTO. My thinking was that Orbital could be a "single-source" supplier that eventually they would be a one-stop shop where Intelsat or SES would purchase a SAT with X amount of transpoders, and Orbital could put that into the correct orbit using Antares.

It looks like a SAT the size of SES-8 is about 3.5 mT, so that's probably out of their range at the moment.
Both Boeing and LM produce satellites and LV they don't fly together, usually. And Antares has a vry high inclination launch site (Wallops) with a very low energy US, which is a very bad stack for GTO. OSC is managed as a business, and their satellite unit does what's best for their bottom line, and the LV unit makes the business they think they can get the better profit of. In the particular case of Antares they'll earn a profit if it only flies for COTS/CRS, and have a chance to get an extra buck by being a Delta II replacement.

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