Ventrater - 14/4/2006 8:56 AMthank you Jim,but the tittle is: "first stage = 3 SRB"this is the first question. The question about the second stage comes after. If you think that the idea is bad, then "why"? I do not think that this first stage would be the most expensive solution.
Jim - 14/4/2006 8:07 AMQuoteVentrater - 14/4/2006 8:56 AMthank you Jim,but the tittle is: "first stage = 3 SRB"this is the first question. The question about the second stage comes after. If you think that the idea is bad, then "why"? I do not think that this first stage would be the most expensive solution.Why is that much thrust needed? They have a short duration, they burn out at 120 seconds. They get you off the pad but don't provide very much impulse. On the Shuttle, the SRB's provide less than 10% of the energy required to get to orbit
Ventrater - 14/4/2006 9:16 AMQuoteJim - 14/4/2006 8:07 AMQuoteVentrater - 14/4/2006 8:56 AMthank you Jim,but the tittle is: "first stage = 3 SRB"this is the first question. The question about the second stage comes after. If you think that the idea is bad, then "why"? I do not think that this first stage would be the most expensive solution.Why is that much thrust needed? They have a short duration, they burn out at 120 seconds. They get you off the pad but don't provide very much impulse. On the Shuttle, the SRB's provide less than 10% of the energy required to get to orbitYes, I know about the 10% (I was thinking: 15%) but if you think about the ariane5, the vulcain2 is only 135 tons thrust. And SRB are not very expensive and they already exist.
Ventrater - 14/4/2006 9:41 AMI do not replace the "vulcian2" with a SRB, not at all. In my idea the second stage is above the first stage. Like the VEGA launcher... or the "stick".
Jim - 14/4/2006 8:59 AMQuoteVentrater - 14/4/2006 9:41 AMI do not replace the "vulcian2" with a SRB, not at all. In my idea the second stage is above the first stage. Like the VEGA launcher... or the "stick".The 3 SRB's have plenty of thrust but not enough impulse. Too much is depending on the second stage. The stick is using a 5 segment SRM because of thisThe costs of the SRB's is a lot higher than $25-33M
Ventrater - 14/4/2006 10:57 AMNo, the reason why NASA consider using a 5 segment is not because of the SRB have not enough impulse but because the SSME is too much difficult to modify (air-starting)!
dmc6960 - 14/4/2006 12:22 PMQuoteVentrater - 14/4/2006 10:57 AMNo, the reason why NASA consider using a 5 segment is not because of the SRB have not enough impulse but because the SSME is too much difficult to modify (air-starting)!No, the reason why NASA switched to a 5 segment is because the only other large upperstage engine they have (when the SSME was deemed impractical) is the J-2. That does not have as much thrust as the SSME, therefore, an extra segment to (try to) make up for it.Why do you insist on this launcher when a rocket scientist has given multiple reasons why its not possible nor practical?
Ventrater - 13/4/2006 3:05 PMSince a long time I think that this launcher could be very interesting: first stage = 3 SRB second stage = 1 RS 68 LEO: 65 tons What do you think ?
edkyle99 - 14/4/2006 12:56 PMQuoteVentrater - 13/4/2006 3:05 PMSince a long time I think that this launcher could be very interesting: first stage = 3 SRB second stage = 1 RS 68 LEO: 65 tons What do you think ? I don't see how you can get a 65 tonne payload. Three SRBs would produce about 4271 tonnes of liftoff thrust. The SRBs appear to work best at a 1.7 thrust to weight ratio (i.e. STS and CLV), so your maximum launch vehicle GLOW would be 2512 tonnes, 1759 tonnes of which would be SRBs. That leaves 753 tonnes for second stage, payload, fairing, interstage, etc. But since the SRBs would burn out at such a low velocity, your RS-68 powered upper stage (lets assume for the sake of argument that an air-start RS-68 would be do-able) would have to have an initial thrust to weight ratio of about 1.0, or perhaps a bit less than 1.0. That limits your upper stage and payload to about 350 tonnes. If the upper stage has a propellant mass fraction of 0.89 (like the planned Crew Launch Vehicle upper stage), then your payload to low earth orbit would only be 35-38 tonnes. 2512 tonnes (heavier than a space shuttle stack) is a lot of launch vehicle for such a relatively small payload. - Ed Kyle
Ventrater - 14/4/2006 2:10 PMQuoteedkyle99 - 14/4/2006 12:56 PMQuoteVentrater - 13/4/2006 3:05 PMSince a long time I think that this launcher could be very interesting: first stage = 3 SRB second stage = 1 RS 68 LEO: 65 tons What do you think ? I don't see how you can get a 65 tonne payload. Three SRBs would produce about 4271 tonnes of liftoff thrust. The SRBs appear to work best at a 1.7 thrust to weight ratio (i.e. STS and CLV), so your maximum launch vehicle GLOW would be 2512 tonnes, 1759 tonnes of which would be SRBs. That leaves 753 tonnes for second stage, payload, fairing, interstage, etc. But since the SRBs would burn out at such a low velocity, your RS-68 powered upper stage (lets assume for the sake of argument that an air-start RS-68 would be do-able) would have to have an initial thrust to weight ratio of about 1.0, or perhaps a bit less than 1.0. That limits your upper stage and payload to about 350 tonnes. If the upper stage has a propellant mass fraction of 0.89 (like the planned Crew Launch Vehicle upper stage), then your payload to low earth orbit would only be 35-38 tonnes. 2512 tonnes (heavier than a space shuttle stack) is a lot of launch vehicle for such a relatively small payload. - Ed Kyle thank you for this clear answer! I have underestimated the low RS 68 isp (when compared whith the J-2). (one SRB + J-2 = 25 tons... and 3 SRB + 3 J-2 = 75 tons, correct?). So, the difference between 75 and 65 is underestimated, okBut the question about a 3 SRB first stage is still open, no?
Jim - 14/4/2006 1:23 PMQuoteVentrater - 14/4/2006 2:10 PMQuoteedkyle99 - 14/4/2006 12:56 PMQuoteVentrater - 13/4/2006 3:05 PMSince a long time I think that this launcher could be very interesting: first stage = 3 SRB second stage = 1 RS 68 LEO: 65 tons What do you think ? I don't see how you can get a 65 tonne payload. Three SRBs would produce about 4271 tonnes of liftoff thrust. The SRBs appear to work best at a 1.7 thrust to weight ratio (i.e. STS and CLV), so your maximum launch vehicle GLOW would be 2512 tonnes, 1759 tonnes of which would be SRBs. That leaves 753 tonnes for second stage, payload, fairing, interstage, etc. But since the SRBs would burn out at such a low velocity, your RS-68 powered upper stage (lets assume for the sake of argument that an air-start RS-68 would be do-able) would have to have an initial thrust to weight ratio of about 1.0, or perhaps a bit less than 1.0. That limits your upper stage and payload to about 350 tonnes. If the upper stage has a propellant mass fraction of 0.89 (like the planned Crew Launch Vehicle upper stage), then your payload to low earth orbit would only be 35-38 tonnes. 2512 tonnes (heavier than a space shuttle stack) is a lot of launch vehicle for such a relatively small payload. - Ed Kyle thank you for this clear answer! I have underestimated the low RS 68 isp (when compared whith the J-2). (one SRB + J-2 = 25 tons... and 3 SRB + 3 J-2 = 75 tons, correct?). So, the difference between 75 and 65 is underestimated, okBut the question about a 3 SRB first stage is still open, no?(one SRB + J-2 = 25 tons... and 3 SRB + 3 J-2 = 75 tons, correct? this is not true. Each case has to be analysed. Thay are not additive. Other than the "unique" stick, SRB's are for assisting liftoff and early flight. A better first stage can be found or designed. Plus the hardware/truss to connect the 3 SRB's would be heavy.
Jim - 14/4/2006 2:23 PM A better first stage can be found or designed. Plus the hardware/truss to connect the 3 SRB's would be heavy.
Jim - 14/4/2006 1:44 PMQuoteJim - 14/4/2006 2:23 PM A better first stage can be found or designed. Plus the hardware/truss to connect the 3 SRB's would be heavy.I said it above.
Ventrater - 14/4/2006 2:52 PMQuoteJim - 14/4/2006 1:44 PMQuoteJim - 14/4/2006 2:23 PM A better first stage can be found or designed. Plus the hardware/truss to connect the 3 SRB's would be heavy.I said it above. Ok, I am not a rocket scientist and I yield to your arguments: it is not a good idea. A 3 SRB first stage is not a good idea. But a last question, please: do you think that the "stick" is not a good idea too?
Jim - 14/4/2006 1:56 PMQuoteVentrater - 14/4/2006 2:52 PMQuoteJim - 14/4/2006 1:44 PMQuoteJim - 14/4/2006 2:23 PM A better first stage can be found or designed. Plus the hardware/truss to connect the 3 SRB's would be heavy.I said it above. Ok, I am not a rocket scientist and I yield to your arguments: it is not a good idea. A 3 SRB first stage is not a good idea. But a last question, please: do you think that the "stick" is not a good idea too?I think it is bad
Ventrater - 14/4/2006 1:10 PMQuoteedkyle99 - 14/4/2006 12:56 PMQuoteVentrater - 13/4/2006 3:05 PMSince a long time I think that this launcher could be very interesting: first stage = 3 SRB second stage = 1 RS 68 LEO: 65 tons What do you think ? I don't see how you can get a 65 tonne payload. Three SRBs would produce about 4271 tonnes of liftoff thrust. The SRBs appear to work best at a 1.7 thrust to weight ratio (i.e. STS and CLV), so your maximum launch vehicle GLOW would be 2512 tonnes, 1759 tonnes of which would be SRBs. That leaves 753 tonnes for second stage, payload, fairing, interstage, etc. But since the SRBs would burn out at such a low velocity, your RS-68 powered upper stage (lets assume for the sake of argument that an air-start RS-68 would be do-able) would have to have an initial thrust to weight ratio of about 1.0, or perhaps a bit less than 1.0. That limits your upper stage and payload to about 350 tonnes. If the upper stage has a propellant mass fraction of 0.89 (like the planned Crew Launch Vehicle upper stage), then your payload to low earth orbit would only be 35-38 tonnes. 2512 tonnes (heavier than a space shuttle stack) is a lot of launch vehicle for such a relatively small payload. - Ed Kyle thank you for this clear answer! I have underestimated the low RS 68 isp (when compared whith the J-2). (one SRB + J-2 = 25 tons... and 3 SRB + 3 J-2 = 75 tons, correct?). So, the difference between 75 and 65 is underestimated, okBut the question about a 3 SRB first stage is still open, no?