You know, I don't understand the choice of a solid U/S. It seems to have all the wrong attributes for an U/S.Solids, IIUC, have a high "dry" weight, since the entire "tank" is thick walled. And in an U/S, every pound wasted is 100% at the expense of payload.
Also, it burns to depletion, so you can't control end-of-burn, so I'd think that precision insertion is problematic.
Lastly, it is not a high ISP solution.
Quote from: Kabloona on 04/17/2013 09:51 pmQuote from: meekGee on 04/17/2013 09:36 pmAnyone familiar with why they went with a solid U/S?IIRC, Antonio said they decided that doing a liquid first stage for the first time (for Orbital) was enough of a challenge, and that trying to simultaneously develop a liquid upper stage would have been biting off more than they could chew. An off-the-shelf solid was a lower technical and schedule risk proposition.And also it was at one point planned to upgrade to a liquid U/S using, IIRC, a Soyuz engine. I believe that plan is shelved at present though (shame!)
Quote from: meekGee on 04/17/2013 09:36 pmAnyone familiar with why they went with a solid U/S?IIRC, Antonio said they decided that doing a liquid first stage for the first time (for Orbital) was enough of a challenge, and that trying to simultaneously develop a liquid upper stage would have been biting off more than they could chew. An off-the-shelf solid was a lower technical and schedule risk proposition.
Anyone familiar with why they went with a solid U/S?
Why is it that Russians launch rockets in the middle of a snow storm / blizzard but in the US we have to worry about low cloud cover?
I note the mission timeline viewgraph at the briefing shows a launch azimuth of 107.8 deg. But the actual hazard area seems to be more like an azimuth of 124 deg, and it needs to turn to an azimuth of 134 deg or so to reach the target inclination.
Yes, since the 30XL will improve performance and the Star 48 can be stacked on top as well. No business case to develop an (expensive) cryo 2nd stage at this point in the game.
It is a Delta II replacement.It wasn't the market that killed F5, it couldn't do a Dragon spacecraft was the reason. The market still exists. See the last Delta II sold.
But isn't that setting the bar pretty low in terms of commercial market?The Delta II is a pretty expensive rocket isn't it?
Quote from: meekGee on 04/18/2013 03:05 amBut isn't that setting the bar pretty low in terms of commercial market?The Delta II is a pretty expensive rocket isn't it?Not commercial market, but market. Delta II also did Globalstar and Iridium constellations.It beat out F9 for 4 launches.
Quote from: happyflower on 04/17/2013 10:16 pmWhy is it that Russians launch rockets in the middle of a snow storm / blizzard but in the US we have to worry about low cloud cover?visibility for Range safety
Are there also concerns about reflected sound, or is Antares too small for that to be a problem?
So this answers the "why" from a few posts ago. A new rocket is always fun, but if the upside is just a delta II replacement then it's less exciting to me than what's in those other forums you complain that I frequent too much...
Quote from: Kabloona on 04/17/2013 10:47 pmYes, since the 30XL will improve performance and the Star 48 can be stacked on top as well. No business case to develop an (expensive) cryo 2nd stage at this point in the game.Well, the business case has to do with the capacity of the overall rocket.Right now, Antares can lift about as much as the F5 was supposed to, but that was a market spot that proved unsuccessful. Part of the reason for this performance is the second stage. (The ISP, 7.3% dry weight)Also, the flip side of the business equation is cost. Development cost may have been lower, but overall I believe the rocket is more expensive.Correct me if I'm wrong, but at the price/capacity of Antares, is it competitive in the commercial arena?
The only issue I see with a solid second stage is that you lose the ability to restart because you really only get a single burn. That means it's near impossible to deploy multiple payloads from the same LV. Of course, since the launcher isn't oversized anyway, that's not an issue.
I took my non-rocket scientist look at the second stage and was actually suprised. The Castor 30 motor actually supplies more total thrust than any equivalent liquid second stage (including both the engine and motor) of comparable launch weight. It wasn't really even close.
Unrelated question - could somebody talk about the orbital mechanics going on here? Apparently, if Friday doesn't work out, it's the last opportunity for 'this part of the month' - why doesn't a launch window to a 51.6 degree orbit open every day?And since this is just a test flight with a dummy payload, what does it matter what orbit they go to? Or is the target orbit driven by the secondary payloads?