An SSTO as "God and Robert Heinlein intended".

[RGClark]

Whel, who can argue about that!
p.s. Sometime I think you are just taking the mick of folk around here, no offence if you aren't of course!
N.

I gather that is British slang? "Mick"?

"Pulling someones leg", perhaps?


Bob Clark

 

[Notebook]

Nicely noticed.

N.

 

[RGClark]

...
the tanking procedure of the ISS for example, is still taking many hours of careful operations: And that just for maximal 1700 kg propellant, which is only corrosive.

Do you have reference for the refueling time for the ISS?

Bob Clark

 

[Urwumpe]

Do you have reference for the refueling time for the ISS?

Bob Clark

"Soyuz - A Universal Spacecraft", it explains the tanking system for the Russian space stations since Salyut 6, including the ISS.

Don't have the book at hand here for exact numbers, but the process is described with some diagrams and explanations.

EDIT: The actual transfer of 815 kg from one ATV to the ISS took 30 minutes according to ESA, but that isn't the full procedure. It involved pressurizing and depressurizing tank pairs, pumping nitrogen from tank bladder to storage tanks, etc. The fuel does not get in contact with any mechanical parts except valves.

EDIT2: And the process is of course fully automatised and controlled from the ground, it is done without any astronaut involvement.

 

[RGClark]

...
EDIT: The actual transfer of 815 kg from one ATV to the ISS took 30 minutes according to ESA, but that isn't the full procedure. It involved pressurizing and depressurizing tank pairs, pumping nitrogen from tank bladder to storage tanks, etc. The fuel does not get in contact with any mechanical parts except valves.

Do you have a link for the ATV refueling procedure?

Bob Clark

 

[Urwumpe]

Do have a link for the ATV refueling procedure?

Not for that, only for the time. But as said above the refueling system is mostly unchanged since Salyut 6. Components and materials have been modernized for the ISS compared to Mir, but not the architecture.

http://www.esa.int/esaMI/ATV/SEMEJGRHKHF_0.html

I recommend reading the ISS reference guide for general information there, it describes the propellant storage system of the ISS in brief.

http://www.nasa.gov/pdf/508318main_ISS_ref_guide_nov2010.pdf

 

[TMac3000]

I believe SSTO is possible, but not with currently technology. We're close, but need to make pretty serious strides in materials and propulsion technology.

 

[Urwumpe]

I believe SSTO is possible, but not with currently technology. We're close, but need to make pretty serious strides in materials and propulsion technology.

I would say we CAN build SSTOs with current technology. But not make SSTOs the economic weapon of mass transportation that some proponents suggest.

This isn't really a matter of technology, but physics and economics. An SSTO would need to compete with TSTOs. And TSTOs are closer to be reuseable for example, than SSTOs, can reach orbit with much lower performance requirements for the subsystems, etc.

You also can't just compare launch vehicles to aircraft - a small launch vehicle requires the energy of a A380 airliner to haul just 7-12 tons of payload into LEO. What you can learn from airliners is logistics and operations - and that for both SSTOs and TSTOs as well. For example, who says that the first stage of a reusable TSTO needs to be made or operated by the same company as the second stage? In engineering, the second stage of a first stage is just payload. Large payload maybe, but payload.

 

[RGClark]

The increasing problem of space junk is getting greater discussion recently:

Space junk at 'tipping point', now getting worse on its own.
More collisions generate more debris, so more collisions.
By Gavin Clarke
Posted in Space, 2nd September 2011 11:18 GMT
http://www.theregister.co.uk/2011/09/02/space_junk_danger/

One company is planning on reusable in-space vehicles to refuel and service satellites. The Air Force favors this since this may also be used to tow inactive satellites out the way of operable satellites, thus reducing the problem of space debris:

Article:
World's First Space Gas Station for Satellites to Launch in 2015.
by Clara Moskowitz, SPACE.com Senior Writer
Date: 15 March 2011 Time: 06:03 PM ET
"Until now, satellites orbiting around Earth have been limited by how much fuel they carry onboard. Once those tanks run dry, the satellites die, sometimes languishing in space as uncontrollable debris that then poses the risk of colliding with other spacecraft.
"The new plan offers the potential not just to extend the lives of working satellites, but to help combat the growing space junk problem. The satellite, called the Space Infrastructure Servicing (SIS) vehicle, is designed not just to transfer more fuel into existing satellites, but to inspect, tow, reposition and make minor repairs to them.
"In addition to its tank of fuel, the refueling satellite will carry a robotic arm that can be used to grab onto satellites and tug at stuck solar array panels, for example, or attempt other minor fixes to broken parts.
'This is a first-time-ever, huge, huge, huge event,' said Andrew Palowitch, director of the Space Protection Program, a joint project of U.S. Air Force Space Command and the National Reconnaissance Office, speaking at a National Research Council workshop on orbital debrislast week.
"Palowitch stressed that the ability to tow or refuel dead satellites in order to steer them out of the way would have a big impact on the growing problem of dangerous space debris clogging the crowded corridors of Earth orbit. [Worst Space Debris Events of All Time]
'In the context of debris removal, this is the absolute best and absolute most fantastic new venture for the entire space community,' he said.
"The refueling satellite will be able to move dead spacecraft to what's called the 'graveyard orbit,' where they are high enough that they should not pose a risk to working satellites, or maneuver them low enough that they break apart in Earth's atmosphere."
http://www.space.com/11135-satellite-refueling-mission-space-debris.html

Then the Air Force recognizes the usefulness of reusable vehicles, when they are in-space. However, the importance of reusable SSTO's is that they could also return these satellites to Earth for repair or salvage.
Remember the old science fiction series Salvage 1:

Salvage 1.
Salvage 1 - Wikipedia, the free encyclopedia

The theme of the show was a small "home made" spaceship was used to return space junk to Earth. I used to think the show was quite implausible because the spaceship went all the way to the Moon and everybody "knows" it takes huge Saturn V sized rockets to do that.
However, as I discussed in post #136 small, low cost SSTO's are indeed possible. And it is a known fact that if you have refueling in LEO then an SSTO can go all the way to the Moon, land, take off, and return to Earth on that one single refueling. So in fact the idea of salvaging spacecraft or satellites from the Moon and/or from GEO is feasible with SSTO's and on-orbit propellant depots.
Then this provides another financial benefit for SSTO's for private developers and for the Air Force. Imagine being able to retrieve satellites, the largest of which can cost upwards of a billion dollars, for reuse or possibly for sale. This does though raise the question of what would be the salvage laws for space.

Here's a link to the full pilot movie:

A single stage vehicle that can travel to the Moon and back is possible now with standard chemical propulsion if you have orbital refueling:

The Coming SSTO's.
http://exoscientist.blogspot.com/2012/05/coming-sstos.html


Bob Clark

 

[RGClark]

I've been arguing that SSTO's are actually easy because how to achieve them is perfectly obvious: use the most weight optimized stages and most Isp efficient engines at the same time, i.e., optimize both components of the rocket equation. But I've recently found it's even easier than that! It turns out you don't even need the engines to be of particularly high efficiency.

SpaceX is moving rapidly towards testing its Grasshopper scaled-down version of a reusable Falcon 9 first stage:

Reusable rocket prototype almost ready for first liftoff.
BY STEPHEN CLARK
SPACEFLIGHT NOW
Posted: July 9, 2012
http://www.spaceflightnow.com/news/n1207/10grasshopper/


SpaceX deserves kudos for achieving a highly weight optimized Falcon 9 first stage at a 20 to 1 mass ratio. However, the Merlin 1C engine has an Isp no better than the engines we had in the early sixties at 304 s, and the Merlin 1D is only slightly better on the Isp scale at 310 s. This is well below the highest efficiency kerosene engines (Russian) we have now whose Isp's are in the 330's. So I thought that closed the door on the Falcon 9 first stage being SSTO.

However, I was surprised when I did the calculation that because of the Merlin 1D's lower weight the Falcon 9 first stage could indeed be SSTO. I'll use the Falcon 9 specifications estimated by GW Johnson, a former rocket engineer, now math professor:


WEDNESDAY, DECEMBER 14, 2011
Reusability in Launch Rockets.
http://exrocketman.blogspot.com/2011/12/reusability-in-launch-rockets.html


The first stage propellant load is given as 553,000 lbs, 250,000 kg, and the dry weight as 30,000 lbs, 13,600 kg. The Merlin 1C mass hasn't been released, but I'll estimate it as 650 kg, from its reported thrust and thrust/weight ratio. The Merlin 1D mass has been estimated to be 450 kg. Then on replacing the 1C with the 1D we save 9*200 = 1,800kg from the dry weight to bring it to 11,800 kg.

The required delta v to orbit is frequently estimated as 30,000 feet per second for kerosene-fueled vehicles, 9,144 m/s. When calculating the delta v your rocket can achieve, you can just use your engines vacuum Isp since the loss of Isp at sea level is taken into account in the 30,000 fps number. Then this version of the Falcon 9 first stage could lift 1,200 kg to orbit:
310*9.81ln(1 + 250/(11.8 + 1.2)) = 9,145 m/s.


Then the Falcon 9 first stage could serve as a proof of principle SSTO on the switch to the Merlin 1D engine.


Bob Clark

 

[Hlynkacg]

And once again you're blithely ignoring the economic and engineering aspects of your own argument.

If it were simply an issue of strapping engine A to stage B SSMEs would be on EVERYTHING.

Likewise an SSTO (that is not reusable) and costs twice as much as TSTO is not an improvement. It is a step backwards.

 

[RGClark]

And once again you're blithely ignoring the economic and engineering aspects of your own argument.
If it were simply an issue of strapping engine A to stage B SSMEs would be on EVERYTHING.
Likewise an SSTO (that is not reusable) and costs twice as much as TSTO is not an improvement. It is a step backwards.

This is a test vehicle, not the actual production vehicle, anymore than the Grasshopper will be or the DC-X was.
This is using the actual Falcon 9 hardware remember with the planned Merlin 1D expected to see first flight on a Falcon 9 next year. Then it's importance would be to demonstrate how easy SSTO is to achieve with engines not even especially efficient on the Isp scale.


Bob Clark

 

[Urwumpe]

The reusable launch vehicle plans of SpaceX are about a TSTO - no SSTO.
A reusable TSTO works even with lower performance engines - that is nothing new in this thread.
The vacuum ISP of 310 seconds for the Merlin 1D is even low for kerolox engines.

 

[Hlynkacg]

Your reply is an complete non-sequiter.

 

[Urwumpe]

Your reply is an complete non-sequiter.

Mine?

 

[Hlynkacg]

No, his.

The vehicle being test or production really has no bearing on the underlying feasability of mating engine A to stage B and as you pointed out the Grasshopper is not even an example of the type of vehicle he's advocating.

Frankly I'm starting to wonder if RGclark is not some sort of sophisticated spam/troll-bot.

The self-referentialism and odd shifts kind of remind me of a turing-test control program.

 

[RGClark]

...
The required delta v to orbit is frequently estimated as 30,000 feet per second for kerosene-fueled vehicles, 9,144 m/s. When calculating the delta v your rocket can achieve, you can just use your engines vacuum Isp since the loss of Isp at sea level is taken into account in the 30,000 fps number. Then this version of the Falcon 9 first stage could lift 1,200 kg to orbit:

310*9.81ln(1 + 250/(11.8 + 1.2)) = 9,145 m/s.

Then the Falcon 9 first stage could serve as a proof of principle SSTO on the switch to the Merlin 1D engine.

We can probably do better than this. The Merlin 1D has a 147,000 lb sea level thrust:

Modified Merlin engine completes full duration firing.
BY STEPHEN CLARK
SPACEFLIGHT NOW
Posted: June 25, 2012
http://www.spaceflightnow.com/news/n1206/25merlin1d/

The gross mass of the Falcon 9 first stage with the Merlin 1D's and a 1.2 mT payload would be 250 + 11.8 + 1.2 = 263 mT, 578,600 lbs. This could be lofted by just 4 of the Merlin 1D's. But the thrust would be just a little over the gross mass resulting in high gravity loss. So let's use 5 Merlins. Subtracting off 4 Merlins makes the dry mass 11,800 - 4*450 = 10,000 kg.
The number of 30,000 fps delta-v for LEO is assuming a T/W ratio common for liquid fueled rockets, in the range 1.1 to 1.2. With all 9 Merlins the T/W ratio would above 2.2. This would result in a much reduced gravity loss. So the required delta-v would be less than the 30,000 fps number, and so actually higher than 1.2 mT could be sent to LEO even in that case.
But let's look at the case of using 5 Merlins. SpaceX has given a vacuum Isp of the Merlin 1D as actually 311 s. Then we could send 3.1 mT to LEO:

311*9.81ln(1 + 250/(10 + 3.1)) = 9,152 m/s.

SpaceX has said though they want to move to a larger version of the Falcon 9 called the Falcon 9 v1.1, in accordance with the Merlin 1D's larger thrust. The Falcon Heavy will use this version's first stage for its core stage and side boosters. SpaceX expects the Falcon 9 v1.1 to be ready by the end of the year.
Elon Musk has said the version 1.1 will be about 50% longer:

Q&A with SpaceX founder and chief designer Elon Musk.
BY STEPHEN CLARK
SPACEFLIGHT NOW
Posted: May 18, 2012
http://www.spaceflightnow.com/falcon9/003/120518musk/

I'll assume this is coming from 50% larger tanks. This puts the propellant load now at 375,000 kg. Interestingly SpaceX says the side boosters on the Falcon Heavy will have a 30 to 1 mass ratio. This improvement is probably coming from the fact it is using the lighter Merlin 1D engines, and because scaling up a rocket actually improves your mass ratio, and also not having to support the weight of an upper stage and heavy payload means it can be made lighter.
So I'll assume for this SSTO version of the Falcon 9 v1.1 the mass ratio is 30 to 1, which makes the dry mass 13 mT. Then this version can lift 6.7 mT to LEO:

311*9.81ln(1 + 375/(13 + 6.7))


Bob Clark

 

[Urwumpe]

Zero is not better than Zero.

 

[RGClark]

...
So I'll assume for this SSTO version of the Falcon 9 v1.1 the mass ratio is 30 to 1, which makes the dry mass 13 mT. Then this version can lift 6.7 mT to LEO:

311*9.81ln(1 + 375/(13 + 6.7))


Bob Clark

I didn't include the answer to that last calculation:

311*9.81ln(1 + 375/(13 + 6.7)) = 9,145 m/s.

Dr. John Schilling has produced a payload estimation program:

Launch Vehicle Performance Calculator.
http://www.silverbirdastronautics.com/LVperform.html

It gives a range of likely values of the payload. I've found the midpoint of the range it specifies is a reasonably accurate estimate to the actual payload for known rockets.
Input the vacuum values for the thrust in kilonewtons and Isp in seconds. The program takes into account the sea level loss. SpaceX gives the Merlin 1D vacuum thrust as 161,000 lbs and vacuum Isp as 311 s:

FALCON 9 OVERVIEW.
http://www.spacex.com/falcon9.php

For the 9 Merlins this is a thrust of 9*161,000*4.46 = 6,460 kN. Use the default altitude of 185 km and the Cape Canaveral launch site, and a 28.5 degree orbital inclination, to match the Cape's latitude.
Input the dry mass of 13,000 kg and propellant mass of 375,000 kg. Then it gives an estimated 7,564 kg payload mass:

Launch Vehicle: User-Defined Launch Vehicle
Launch Site: Cape Canaveral / KSC
Destination Orbit: 185 x 185 km, 28 deg
Estimated Payload: 7564 kg
95% Confidence Interval: 3766 - 12191 kg

This may be enough to launch the Dragon capsule, depending on the mass of the Launch Abort System(LAS).


Bob Clark

 

[Urwumpe]

What did you use as sea-level specific impulse for the Merlin 1D?