Why is not a SSTO useful today?

[fredinno]

1 hour ago, Red Iron Crown said:

I don't think many customers would want to wait 2 years after launch for their investment to reach its useful orbit. Better to pay more (possibly) for a conventional rocket and get that satellite earning that much sooner.

He was using hyperbole.

[Nothalogh]

SSTOs are only practical for hauling passengers to and from LEO. Big honkin boosters are for cargo 

[wumpus]

19 hours ago, Red Iron Crown said:

I don't think many customers would want to wait 2 years after launch for their investment to reach its useful orbit. Better to pay more (possibly) for a conventional rocket and get that satellite earning that much sooner.

Commercial satellite launchers wouldn't want such a thing.  You'd be surprised how often NASA science probes tend to have to wait years for a launch.  My guess is that once the thing is up and in space, it is that much harder to cut the program.  The other big issue is if the payload is in the Van Allen belts for two years.  What type of shielding do you need, and could you put the whole thing into GTO (or escape velocity) if you didn't have all that shielding?

Another thing to remember is that two years to GTO is two years to the Moon (and L2) or three years to Mars.  Having bulk fuel (read solid/hybrid/other long term rockets)/cargo ready and waiting at those locations (for roughly the cost of LEO) changes things a bit (like forget the BFR and go to Mars using a bunch of Falcon Heavys).

[ModZero]

5900 is the proposed starting orbit because that's outside the lower VA belt (that's what the manual says). Of course if we go into, erm, "advanced concepts", we could just discharge the belts ;-P

[ModZero]

Oh, and to defend the EP thing a bit, it's actually something we do already, for example this is a presentation on the subject from Eutelsat, and this article mentions an accurate delivery helped them save weeks off the delivery time — so the entire thing isn't unheard of.

[fredinno]

On 1/14/2016 at 5:13 PM, Nothalogh said:

SSTOs are only practical for hauling passengers to and from LEO. Big honkin boosters are for cargo 

No, adding cargo to the mix increases launch numbers dramatically, making an SSTO more viable.

14 hours ago, wumpus said:

Commercial satellite launchers wouldn't want such a thing.  You'd be surprised how often NASA science probes tend to have to wait years for a launch.  My guess is that once the thing is up and in space, it is that much harder to cut the program.  The other big issue is if the payload is in the Van Allen belts for two years.  What type of shielding do you need, and could you put the whole thing into GTO (or escape velocity) if you didn't have all that shielding?

Another thing to remember is that two years to GTO is two years to the Moon (and L2) or three years to Mars.  Having bulk fuel (read solid/hybrid/other long term rockets)/cargo ready and waiting at those locations (for roughly the cost of LEO) changes things a bit (like forget the BFR and go to Mars using a bunch of Falcon Heavys).

I would use the highest thrust IONs available (like the ones for ARM) and cap the transit time to a week, tops.

11 hours ago, ModZero said:

Oh, and to defend the EP thing a bit, it's actually something we do already, for example this is a presentation on the subject from Eutelsat, and this article mentions an accurate delivery helped them save weeks off the delivery time — so the entire thing isn't unheard of.

What's EP?

[Nibb31]

Electric propulsion ?

[fredinno]

16 minutes ago, Nibb31 said:

Electric propulsion ?

Thank you.

[Nothalogh]

20 hours ago, fredinno said:

No, adding cargo to the mix increases launch numbers dramatically, making an SSTO more viable.

It also makes them less viable from an engineering perspective.

Cargo is often higher volume per unit of value, compared to humans.

 

We can launch comsats and toilet paper on top of a stack of SRBs, humans not so much.

[fredinno]

1 hour ago, Nothalogh said:

It also makes them less viable from an engineering perspective.

Cargo is often higher volume per unit of value, compared to humans.

 

We can launch comsats and toilet paper on top of a stack of SRBs, humans not so much.

Or design the rocket for cargo, but also be able to carry people. Any SSTO will be liquid fuelled, so it will be much more friendly to humans than solids.

[Exploro]

On 1/13/2016 at 0:28 PM, fredinno said:

Like the Shuttle-Centaur plans with the Shuttle? Yeah, good luck caring flammable material inside an enclosed cargo bay...

Lofting flammable materials enclosed in the cargo bay was what the Space Shuttle did even after post-Challenger. Remember the Inertial Upper Stage employed on subsequent shuttle mission; like Magellan or Galileo, were stuffed with flammable materials.

What made NASA reconsider using Centaur for the shuttle was the challenge of purging the upper stage of fuel in the event of an emergency. There wouldn't be a way to quickly accomplish this. Thus carriage of the IUS was deemed safer; but it is still a cylinder filled with volatile materials.

Also consider that Centaur was like the Atlas Rocket; it needed to be pressurized to maintain structural integrity; either with inert gas while in storage or with fuel during flight. A proposed reusable upper stage for the Skylon might not necessarily require that the tanks be filled with any propellant during launch. It's conceivable propellants could be loaded into the upper stage while inorbit from the Skylon's own propellant tanks.

[fredinno]

1 hour ago, Exploro said:

Lofting flammable materials enclosed in the cargo bay was what the Space Shuttle did even after post-Challenger. Remember the Inertial Upper Stage employed on subsequent shuttle mission; like Magellan or Galileo, were stuffed with flammable materials.

What made NASA reconsider using Centaur for the shuttle was the challenge of purging the upper stage of fuel in the event of an emergency. There wouldn't be a way to quickly accomplish this. Thus carriage of the IUS was deemed safer; but it is still a cylinder filled with volatile materials.

Also consider that Centaur was like the Atlas Rocket; it needed to be pressurized to maintain structural integrity; either with inert gas while in storage or with fuel during flight. A proposed reusable upper stage for the Skylon might not necessarily require that the tanks be filled with any propellant during launch. It's conceivable propellants could be loaded into the upper stage while inorbit from the Skylon's own propellant tanks.

So? Solids aren't fluids, and won't expand quickly. LH2 will. Also, Solids have abysmal payload capacity. But your idea might work. If things go really bad, just eject the stage. Only problem is increased complexity, and higher cost due to more pumps.

[Interplanetary Engineer]

It'd be really nice if our economy system was based on the coolness of an idea, in wich case we'd already be flying around in SKYLONs all the time.
Sadly, that isn't how it works in reality, and so spaceflight will probably just be dominated by some partially-reusable or overall chapskate rockets.

[fredinno]

6 hours ago, Interplanetary Engineer said:

It'd be really nice if our economy system was based on the coolness of an idea, in wich case we'd already be flying around in SKYLONs all the time.
Sadly, that isn't how it works in reality, and so spaceflight will probably just be dominated by some partially-reusable or overall chapskate rockets.

If it was dominated by coolness factor, we would have dysfunctional machines and budget-sucking that were only created because it was cool, and not because it was practical. Like solar roadways.