Quote from: Star One on 01/27/2014 11:23 amSo why does this need the 522 configuration yet DC can use the no doubt cheaper 402 configuration?Do we know that CST-100 will use the 522? How do we know it's not the 422?
So why does this need the 522 configuration yet DC can use the no doubt cheaper 402 configuration?
The capsule will launch on a version of the Atlas 5 known as the 422 model - with a two-engine Centaur and two solid rocket boosters - in the launcher's catalog of configurations tailored to the size and destination of the payload for each launch, according to a Boeing spokesperson.
Also don't know why people think this hurts CST. They already needed at least 1 SRB, so adding another doesn't change much (a few $). If DC has mass growth they'll probably end up doing the same thing.
Quote from: arachnitect on 01/27/2014 06:04 pmAlso don't know why people think this hurts CST. They already needed at least 1 SRB, so adding another doesn't change much (a few $). If DC has mass growth they'll probably end up doing the same thing.DC is still supposed to use the 402, from all that is currently known. I was not aware that the CST was originally supposed to use the 412. I thought it was going to be the 402 just like the DC.
Quote from: Elmar Moelzer on 01/27/2014 06:29 pmQuote from: arachnitect on 01/27/2014 06:04 pmAlso don't know why people think this hurts CST. They already needed at least 1 SRB, so adding another doesn't change much (a few $). If DC has mass growth they'll probably end up doing the same thing.DC is still supposed to use the 402, from all that is currently known. I was not aware that the CST was originally supposed to use the 412. I thought it was going to be the 402 just like the DC.Right - my question still stands, does the addition of the SRB's (only about $5 million, not that much considering) change the reliability of the Atlas V.
Quote from: BrightLight on 01/27/2014 06:35 pmQuote from: Elmar Moelzer on 01/27/2014 06:29 pmQuote from: arachnitect on 01/27/2014 06:04 pmAlso don't know why people think this hurts CST. They already needed at least 1 SRB, so adding another doesn't change much (a few $). If DC has mass growth they'll probably end up doing the same thing.DC is still supposed to use the 402, from all that is currently known. I was not aware that the CST was originally supposed to use the 412. I thought it was going to be the 402 just like the DC.Right - my question still stands, does the addition of the SRB's (only about $5 million, not that much considering) change the reliability of the Atlas V.Well, it doesn't /improve/ the reliability.
It might improve the reliability of the overall system. since there is spare thrust in the first stage. As long as they already had 1 solid, I don't see adding a second solid making it any less safe.
Quote from: Lurker Steve on 01/27/2014 07:17 pmIt might improve the reliability of the overall system. since there is spare thrust in the first stage. As long as they already had 1 solid, I don't see adding a second solid making it any less safe.Statistics. That's why. You are adding a possible failure point.How does that spare thrust help you? There is no scenario where a first stage engine out (or booster out) is recoverable.Atlas V doesn't launch with more SRBs than needed.
...adding another SRB doesn't improve reliability compared to a similar vehicle launched without one. How is this really in question?I agree it probably has negligible effect on reliability, though. Atlas V is one of the most reliable launch vehicles on record.
Quote from: Robotbeat on 01/27/2014 08:05 pm...adding another SRB doesn't improve reliability compared to a similar vehicle launched without one. How is this really in question?I agree it probably has negligible effect on reliability, though. Atlas V is one of the most reliable launch vehicles on record.I wonder which has larger, albeit small incremental, reduction effect on reliability - one extra solid motor or one extra RL10? My bet would be RL10. - Ed Kyle
The wind tunnel images for both CST-100 and Dream Chaser (images attached) show an Atlas 4xx; no SRB shown but may be on other side. Edit: presumably that's a 4x2 as both CST-100 and DC have stated DEC is required.
It improves reliability by increasing your mass margin on the spacecraft (can use heavier components, add redundancy, no need to mess around with composites). Also CST doesn't have to use its LAS to get into orbit like DC does.
Quote from: arachnitect on 01/27/2014 07:33 pmIt improves reliability by increasing your mass margin on the spacecraft (can use heavier components, add redundancy, no need to mess around with composites). Also CST doesn't have to use its LAS to get into orbit like DC does.You are mixing apples and oranges. 1. The launch vehicle reliability is lowered2. And you can't say it increases spacecraft reliability. It doesn't matter if the spacecraft doesn't make into orbit.