SpaceX News

[happyjack27]

What payload has 450 tons?!!!

you mean what rocket can carry such a payload?

spacex's proposed ITS.
i thought that's what we were all talking about.

No, I mean who needs such a huge payload?! The cost per kg to orbit is one thing, but the cost per launch is another. My proposed ITS- Tanker based SSTO RLV beats the full ITS stack on cost per launch by quite a large margin.
The only time you need 450 tons into orbit at one time is if you want to launch a space station in one go, or if you want to conduct large scale colonization of a planetary body the way Musk wants to do it. Any other time, you will fly mostly empty and your cost/kg will go through the roof.

you can launch multiple satellites.

you need only launch twice the payload of your ssto to make it cheaper to use a two stage.

[Skipjack]

you can launch multiple satellites.

you need only launch twice the payload of your ssto to make it cheaper to use a two stage.

And this is where you err. You can not just launch multiple satellites into the same orbit. There are things like launch windows, orbital trajectories, slots, etc.
Do you know how hard it is for Arianespace to even fill ArianeV for every launch?

[happyjack27]

you can launch multiple satellites.

you need only launch twice the payload of your ssto to make it cheaper to use a two stage.

And this is where you err. You can not just launch multiple satellites into the same orbit. There are things like launch windows, orbital trajectories, slots, etc.
Do you know how hard it is for Arianespace to even fill ArianeV for every launch?

10 seconds on the google:

"How does a single rocket place multiple satellites into orbit?" - http://space.stackexchange.com/question ... into-orbit

"India launches 20 satellites in single mission" - http://www.bbc.com/news/world-asia-india-36593855

[hanelyp]

Launching many satellites at once works a lot better when they're going into the same orbit, or at least the same orbital plane.

[krenshala]

For SSTOs lightweight structures are generally more important than Isp.

the rocket equation is:

deltav = isp * ln(full mass / empty mass).

now algebraically this can be rewritten:

deltav = isp * ln(full mass) - isp * ln(empty mass).

so while deltav grows linearly with isp, it only grows logarithmically with mass reduction. meaning to get the same amount of improvement as raising the isp, you'd have to decrease the mass -- the majority of which is your payload -- exponentially.

The rocket equation is : Δv (in m/s) = 9.8 * Isp * ln( wetmass / drymass)

The rest I agree with.

[krenshala]

Launching many satellites at once works a lot better when they're going into the same orbit, or at least the same orbital plane.

If the satellites have the fuel for it, plane changes are also an option (and lower requirements the larger the orbit). Its still easier, and cheaper, to have at least similiar intended inclinations for all the payloads in a single rocket.

[happyjack27]

Launching many satellites at once works a lot better when they're going into the same orbit, or at least the same orbital plane.

If the satellites have the fuel for it, plane changes are also an option (and lower requirements the larger the orbit). Its still easier, and cheaper, to have at least similiar intended inclinations for all the payloads in a single rocket.

If the satellites OR the rocket have the fuel for it.

While it would be more fuel efficient and thus mass efficient for the satellites to more to their orbits - and if they can do so with ion thrusters, it's WAY more mass efficient - the rocket still has literally 100's of tons of fuel. It could hand deliver them itself, one at a time, on the most efficient course. then do the hoki-poki and turn itself around.

(that last step isn't strictly necessary.)

regardless, yeah, inclination is the real killer. orbit phase is simple and cheap to fix. i know this, of course, from playing kerbal space program.

[happyjack27]

A reduction in dry mass by a ton means a direct increase of payload by a ton.

taking the falcon 9 as an example - its dry mass is 25 tons. so a reduction in dry mass of a ton is a 4% reduction.
If instead we increased the isp by 4% (from 360 to 374.4), the falcon 9 would be able to carry 4.5 additonal tons to LEO.

examined differently: to carry that extra ton, without reducing the dry mass, you'd have to increase the isp by 1%. So at those initial values, a 1% increase in isp (from 360 to 364) does the same as a 4% reduction in dry mass.

[Tom Ligon]

More on the SpaceX-ULA story. This one has an aerial map view that confirms they are interested in the building I thought they were. What is still missing is any indication from SpaceX of exactly where in the public images one might find the mysterious shadow and spot. The location of the ULA "SMARF" building is in line with my proposed location for the camera from which we got the video, so it is tough to see what it would have to do with the mystery object traversing the field of view from right to left.

http://www.businessinsider.com/spacex-s ... ly-2016-10

[Skipjack]

A reduction in dry mass by a ton means a direct increase of payload by a ton.

taking the falcon 9 as an example - its dry mass is 25 tons. so a reduction in dry mass of a ton is a 4% reduction.
If instead we increased the isp by 4% (from 360 to 374.4), the falcon 9 would be able to carry 4.5 additonal tons to LEO.

examined differently: to carry that extra ton, without reducing the dry mass, you'd have to increase the isp by 1%. So at those initial values, a 1% increase in isp (from 360 to 364) does the same as a 4% reduction in dry mass.

That increase in Isp is not that easy, though. Anyway, I have Philip Bono and Gary Hudson on my side regarding the argument of light structures vs Isp.
http://www.spacefuture.com/archive/hist ... tems.shtml

10 seconds on the google:

"How does a single rocket place multiple satellites into orbit?" - http://space.stackexchange.com/question ... into-orbit

"India launches 20 satellites in single mission" - http://www.bbc.com/news/world-asia-india-36593855

Congratulations you have discovered the payload adapter for multiple satellites! This is great if you have satellites that go into the same orbital inclination like they do in LEO constellations. Falcon9 has launched several of those as well. Sure, you can occasionally have a set of satellites that go into the same orbit, but even with the constellations, you can't launch more than a few at a time. Look at SpaceX's launch manifest!

I also have Arianespace on my side regarding the problem with your logic that having one launch with 20 or more satellites is cheaper and better. It is simply not the case. This is why Ariane 6 will have less payload than Airane 5 and will focus on cost reduction instead.
I will challenge you to find 20+ satellites in one year that need to be launched into a single inclination, or even close. Maybe with some of the large LEO constellations...
Anyway, this discussion is starting to bore me. Do your bloody homework on orbital mechanics and why super heavy lifters are rarely cost effective. The SLS will be catastrophic from a cost POV.

Also look into launch rates and how those affect cost for RLVs.

[happyjack27]

A reduction in dry mass by a ton means a direct increase of payload by a ton.

taking the falcon 9 as an example - its dry mass is 25 tons. so a reduction in dry mass of a ton is a 4% reduction.
If instead we increased the isp by 4% (from 360 to 374.4), the falcon 9 would be able to carry 4.5 additonal tons to LEO.

examined differently: to carry that extra ton, without reducing the dry mass, you'd have to increase the isp by 1%. So at those initial values, a 1% increase in isp (from 360 to 364) does the same as a 4% reduction in dry mass.

That increase in Isp is not that easy, though. Anyway, I have Philip Bono and Gary Hudson on my side regarding the argument of light structures vs Isp.
http://www.spacefuture.com/archive/hist ... tems.shtml

And I have math.

[happyjack27]

10 seconds on the google:

"How does a single rocket place multiple satellites into orbit?" - http://space.stackexchange.com/question ... into-orbit

"India launches 20 satellites in single mission" - http://www.bbc.com/news/world-asia-india-36593855

Congratulations you have discovered the payload adapter for multiple satellites! This is great if you have satellites that go into the same orbital inclination like they do in LEO constellations. Falcon9 has launched several of those as well. Sure, you can occasionally have a set of satellites that go into the same orbit, but even with the constellations, you can't launch more than a few at a time. Look at SpaceX's launch manifest!

I also have Arianespace on my side regarding the problem with your logic that having one launch with 20 or more satellites is cheaper and better. It is simply not the case. This is why Ariane 6 will have less payload than Airane 5 and will focus on cost reduction instead.
I will challenge you to find 20+ satellites in one year that need to be launched into a single inclination, or even close. Maybe with some of the large LEO constellations...
Anyway, this discussion is starting to bore me. Do your bloody homework on orbital mechanics and why super heavy lifters are rarely cost effective. The SLS will be catastrophic from a cost POV.

Also look into launch rates and how those affect cost for RLVs.

If one is only launching one satellite into orbit, it is more economical to use a two-stage reusable system, scaled to the approximate payload.

unless you use air-breathing engines for a dramatic increase in isp, and have a good total reuses / total cost ratio to properly amortize the initial investment.

[Skipjack]

If one is only launching one satellite into orbit, it is more economical to use a two-stage reusable system, scaled to the approximate payload.
unless you use air-breathing engines for a dramatic increase in isp, and have a good total reuses / total cost ratio to properly amortize the initial investment.

No, it is not. The economy of RLVs is driven by:
- Development cost
- Cost to build
- Cost of refurbishment
- Flight rate
- number of reuses

Isp is not a major contributor to cost. It enables more payload and a higher delta-v but that is a comparably minor factor when you already have at least 20 t to LEO.

Air breathing only potentially(!) enables more payload and higher orbits without an orbital tug or some other form of second stage (e.g. more fuel in the satellite so it can get there on its own).
Like the Merlins, the Raptor engines might experience a slight increase in Isp (and thrust) over time as they figure out their margins and other ways to optimize them. Though I doubt that the improvements will be as big as they have been with Merlin. Still, this is something that will potentially benefit the proposed SSTO in the future.

[Skipjack]

And I have math.

And I showed you my math earlier. A very conservatively estimated 20 tonnes to LEO with plenty of margins to go in a LV with minimal refurbishment (and therefore very high flight rate and low operating cost) and a launch cost of less than 2.4 million.
This is as close to airliner like operations as it will get.

[happyjack27]

If one is only launching one satellite into orbit, it is more economical to use a two-stage reusable system, scaled to the approximate payload.
unless you use air-breathing engines for a dramatic increase in isp, and have a good total reuses / total cost ratio to properly amortize the initial investment.

No, it is not. The economy of RLVs is driven by:
- Development cost
- Cost to build
- Cost of refurbishment
- Flight rate
- number of reuses

Small two stage compared to Massive (ITS tanker) SSTO:
- Development cost - well clearly there'd be some, but it's not new territory here.
- Cost to build - smaller, fewer engines, less materials, means lower cost to build. also lower stage doesn't need heat shields
- Cost of refurbishment - as above, lower costs
- Flight rate - once per satelite, either way
- number of reuses - the lower stage would have a lot more reuse, flight stresses are much less - lower speed, doesn't need heat shields

so... tie,win,win,tie,win.

Isp is not a major contributor to cost. It enables more payload and a higher delta-v but that is a comparably minor factor when you already have at least 20 t to LEO.

...or you could use it to build a smaller rocket. reducing both cost to build and cost to refurbish.

Air breathing only potentially(!) enables more payload and higher orbits without an orbital tug or some other form of second stage (e.g. more fuel in the satellite so it can get there on its own).

Everything "only potentially" does anything. A rocket "only potentially" makes it to LEO.

Like the Merlins, the Raptor engines might experience a slight increase in Isp (and thrust) over time as they figure out their margins and other ways to optimize them. Though I doubt that the improvements will be as big as they have been with Merlin. Still, this is something that will potentially benefit the proposed SSTO in the future.

Benefit how? Isp is not a major contributor to cost. It enables more payload and a higher delta-v but that is a comparably minor factor when you already have at least 20 t to LEO.