4 ms·

All solid LV's haven't really been cheaper than liquids in the general case, the motors themselves tend to be quite expensive. Also, a single SRB is never suff

All solid LV's haven't really been cheaper than liquids in the general case, the motors themselves tend to be quite expensive. Also, a single SRB is never sufficient, even with 0 payload a very large solid doesn't have the propellant-mass ratio to get even close to orbit. Something like Pegasus or (I think) Athena 1 were 3 stage designs. Being solid helps simplify the ground support infrastructure and launch pad, whose costs don't scale down well. With an all-solid, something like the Kodiak launch complex is feasible, an extremely simple assembly building + pad.

mrfusion 12y ago
Interesting. So how did they help the shuttle?
- Solarsail 12y ago
  The shuttle used them as early-flight boosters. Same trick used by Ariane V, Titan III / IV, Delta II / III / IV, endless other big vehicles... They are much cheaper to develop per thrust than liquids (They are expensive per size, but scale up to higher thrusts well), and you often want most of your thrust early on rather than later. Solid boosters you ditch after 30s or a minute raise your T/W ratio so you don't loose as much fuel to gravity losses, and get your more efficient but less powerful liquids into the upper atmosphere. Both Ariane V and Shuttle typify this, with almost all liftoff thrust from the solids, and a small, expensive hydrogen-burning engine continuing to most of orbital velocity. For the shuttle, this was aimed at reusablility, they could do most of their work on expensive engines, and not need to pay that cost every flight. Ariane did it so it could make near-orbit with only engines it lit on the pad, for reliability sake. (Planned for the Hercules spaceplane, which wouldn't have used the upper stages that satellites would eventually use.)
Gravityloss 12y ago
But you can't fuel up the solids on the pad. You must cast the propellant into the casings at the factory, potentially on the other side of the globe if that's where you have the nearest capable industry. This means you need fire safety everywhere, and heavy ground equipment too for lifting and attaching and assembling the solid rockets. Meanwhile, you can fuel a liquid rocket at the pad, meaning it's empty and light and can not explode or burn during transport and handling. So solids cause heavier rocket ground infrastructure and more danger. Of course, with liquids you need the fueling infrastructure on the pad. It probably comes to a question, not only of scale, but also of launch rate. In theory you could have mobile trucks fueling missiles here and there. That's how you do it at ship ports where you don't want to invest in ground infrastructure.

mrfusion 12y ago

Interesting. So how did they help the shuttle?

Solarsail 12y ago
The shuttle used them as early-flight boosters. Same trick used by Ariane V, Titan III / IV, Delta II / III / IV, endless other big vehicles... They are much cheaper to develop per thrust than liquids (They are expensive per size, but scale up to higher thrusts well), and you often want most of your thrust early on rather than later. Solid boosters you ditch after 30s or a minute raise your T/W ratio so you don't loose as much fuel to gravity losses, and get your more efficient but less powerful liquids into the upper atmosphere. Both Ariane V and Shuttle typify this, with almost all liftoff thrust from the solids, and a small, expensive hydrogen-burning engine continuing to most of orbital velocity. For the shuttle, this was aimed at reusablility, they could do most of their work on expensive engines, and not need to pay that cost every flight. Ariane did it so it could make near-orbit with only engines it lit on the pad, for reliability sake. (Planned for the Hercules spaceplane, which wouldn't have used the upper stages that satellites would eventually use.)

Gravityloss 12y ago

But you can't fuel up the solids on the pad. You must cast the propellant into the casings at the factory, potentially on the other side of the globe if that's where you have the nearest capable industry. This means you need fire safety everywhere, and heavy ground equipment too for lifting and attaching and assembling the solid rockets. Meanwhile, you can fuel a liquid rocket at the pad, meaning it's empty and light and can not explode or burn during transport and handling. So solids cause heavier rocket ground infrastructure and more danger. Of course, with liquids you need the fueling infrastructure on the pad. It probably comes to a question, not only of scale, but also of launch rate. In theory you could have mobile trucks fueling missiles here and there. That's how you do it at ship ports where you don't want to invest in ground infrastructure.