I find it curious that so many rockets do parallel staging. Apart from ground-starting the engines on the core there don't seem to be any obvious advantages. You save some thrust on the first stage (often little because the core uses hydrolox) but you lose some performance (more dry mass at separation, lower engine ISP).Anything else?
the main advantage
the attraction of parallel staging is simply [...]
less gravity loss early on because of the T/W, (for a given total "installed thrust?") of this arrangement, as getting through the vertical component quickly is always preferable.
Are rockets designed with the intent of using solid rocket boosters from the beginning? My assumption was that solids are expensive and are designed only to be used on rare heavy payloads when the rocket needs an extra boost from the pad. That way the standard rocket don't have excesses capacity i.e. lower cost. How wrong am I?
Quote from: Hirox on 05/17/2016 09:54 pmAre rockets designed with the intent of using solid rocket boosters from the beginning? My assumption was that solids are expensive and are designed only to be used on rare heavy payloads when the rocket needs an extra boost from the pad. That way the standard rocket don't have excesses capacity i.e. lower cost. How wrong am I?Depends on the rocket. The Space Shuttle and Delta2 both require solids to leave the pad (they're TWR<1 without). Delta4 and AtlasV, for instance, can optionally use solids if they need extra oomph.
When the Atlas V rocket was designed, why did they decide to use 2 rd180 instead of 3? An extra engine would remove the need for solids which in turn could reduce their cost by removing a supplier and increasing their production of the engine bringing the cost down. Does one extra engine cost significantly more than the occasional solid rocket booster? I've been thinking of the falcon 9 and their "one size fits all" approach and been wondering if, for example, the falcon 9 rocket never was designed and they went with the Falcon 5 instead, would it make economic sense for them to occasionally use solid rocket boosters?
Quote from: Hirox on 05/17/2016 09:54 pmAre rockets designed with the intent of using solid rocket boosters from the beginning? My assumption was that solids are expensive and are designed only to be used on rare heavy payloads when the rocket needs an extra boost from the pad. That way the standard rocket don't have excesses capacity i.e. lower cost. How wrong am I?Solid rockets are actually cheaper to produce and operate than liquid stages of similar performance. What also helps is that solids are the best way to launch nuclear bombs at other continents, so most of their development and production investments are already made for the military.
It seems many companies are working on methane engines. Would a methane 1st stage be ruled out, or is RP1 too good fuel of choice density/performance wise.
Quote from: jabe on 06/25/2016 01:31 pmIt seems many companies are working on methane engines. Would a methane 1st stage be ruled out, or is RP1 too good fuel of choice density/performance wise.http://spacelaunchreport.com/vulcan.htmlThe successor to the Atlas V and Delta IV rockets is probably going to have a methane first stage.
is it lack of maturity of the tech for methane that it isn't used more?
How did the Juno space probe reach 165,000 MPH?