An SSTO as "God and Robert Heinlein intended".

[RGClark]

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

I contacted the author of the program John Schilling via email about what you should input for the thrust and Isp of the engines. He said you should just use the vacuum values. He said the program takes into account these are both reduced at sea level.
Of course not every engine is going to be reduced to the same extent at sea level operation, which adds some additional inaccuracy to the program.
I'll ask him if he could add the option where you are able to specify the sea level thrust and Isp.

Bob Clark

 

[RGClark]

...

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

According to this report from 2010, ESA was considering plans to use the Orion on the Ariane 5 to get a European manned spaceflight capability:

French govt study backs Orion Ariane 5 launch.
By Rob Coppinger
on January 8, 2010 4:45 PM
http://www.flightglobal.com/blogs/hyperbola/2010/01/french.html

This would cost several billion dollars to man-rate the Ariane 5. I have to believe the solid rocket boosters, which can not be shut down when started, play a significant role in that high cost.
However, the ESA has now given up on an indigenous manned spaceflight capability because of the estimated billion dollar cost to man-rate the full Ariane 5 system:

WSJ: Europe Ends Independent Pursuit of Manned Space Travel.
"LE BOURGET, France—Europe appears to have abandoned all hope of
independently pursuing human space exploration, even as the region's
politicians and aerospace industry leaders complain about shrinking
U.S. commitment to various space ventures.
"After years of sitting on the fence regarding a separate, pan-
European manned space program, comments by senior government and
industry officials at the Paris Air Show here underscore that budget
pressures and other shifting priorities have effectively killed that
longtime dream."
http://www.orbiter-forum.com/showthread.php?t=23006

In contrast, the Ariane 5 core stage with an added, second Vulcain engine could serve as a SSTO to carry a manned capsule to orbit. JAXA was able to add a second cryogenic engine to their H-IIa rockets first stage, which is about the same size as that of the Ariane 5, for less than a $250 million dollar development cost:

Rocketing to the future.
http://www.gov-online.go.jp/pdf/hlj_ar/vol_0027e/05-07.pdf

Mitsubishi Heavy To Invest In Next-Generation Rocket.
by Staff Writers
Tokyo, Japan (AFX) Jun 14, 2006
http://www.spacedaily.com/reports/Mitsubishi_Heavy_To_Invest_In_Next_Generation_Rocket.html

The $250 million cost number I'm getting from the exchange rate from yen to dollars used in the second article. It is important to note about $50 million of this was used to widen the tanks, which wouldn't be needed in the Ariane 5 case. So we can estimate the development cost without widened tanks as less than $200 million. This is about the amount of the subsidy that the ESA gives to ArianeSpace every year. But this would be for a 4 year development, judging by the JAXA case, so would only be $50 million a year.

In the calculations for this multi-Vulcain Ariane core stage, I used this page for the specifications on the Ariane:

Space Launch Report: Ariane 5 Data Sheet.
http://www.spacelaunchreport.com/ariane5.html#config

For the Vulcain 2 specifications, I've seen different numbers in different sources, though close to each other. I'll use this source:

Vulcain 2.
http://www.astronautix.com/engines/vulcain2.htm

I'll also use the earlier Ariane 5 "G" version that is lighter than the current "E" version to be lofted by two Vulcains without side boosters. According to the SpaceLaunchReport page it had a 170 mT gross mass for the core at a 158 mT propellant load, giving a 12 mT dry mass.
According to the Astronautix page, Vulcain 2 has a 434 s vacuum Isp and 1350 kN vacuum thrust. So two will have a 2700 kN vacuum thrust. The Vulcain's mass is listed as 1,800 kg. So adding another will bring the stage dry mass to 13,800 kg.
Now input this data into Schilling's calculator. Select again default residuals and select "No" for the "Restartable Upper Stage?" option. Select the Kourou launch site for this Ariane 5 core rocket. For the orbital inclination, I input 5.2 degrees. I gather Schilling uses this for Kourou's latitude since deviating from this decreases the payload. I chose also direct ascent for the trajectory.

Then the result I got was 7,456 kg(!) to orbit:

================================
Mission Performance:
Launch Vehicle: User-Defined Launch Vehicle
Launch Site: Guiana Space Center (Kourou)
Destination Orbit: 185 x 185 km, 5 deg
Estimated Payload: 7456 kg
95% Confidence Interval: 4528 - 10898 kg
================================

Interestingly, the payload capability of the Falcon 9 v1.1 first stage and of this two-Vulcain Ariane 5 core stage would be about the same as SSTO's.



Bob Clark

 

[Hlynkacg]

Did you even check the stand-off diameter of a Vulcain before running off with your calculator?

 

[N_Molson]

Did you even try with Velcro Rockets ?

 

[RGClark]

Did you even try with Velcro Rockets ?

I'd love to try that, but I still haven't taken the time to learn it. Is it a long learning curve?

Bob Clark

 

[N_Molson]

Not at all. Basically, you just have to input the correct numbers in the configuration files. Just take any rocket that comes with the package and replace the numbers by your own, as a theoretical experiment.

 

[RGClark]

Not at all. Basically, you just have to input the correct numbers in the configuration files. Just take any rocket that comes with the package and replace the numbers by your own, as a theoretical experiment.

Where are the configuration files and how do you execute the program?

Bob Clark

 

[Cosmic Penguin]

Where are the configuration files and how do you execute the program?

Bob Clark

Download the Velcro Rockets add-on and read the documentation.

GPS

 

[T.Neo]

Velcro Rockets is a really fun and easy addon to play around with. There's nothing intimidating about it; it's all based on .cfg and .scn files, the functions are well described in the documentation and the values should make sense to anyone with a good idea of launch vehicle comparisons.

I've spent many an afternoon creating all sorts of interesting combinations (as well as all-new stages).

 

[RGClark]

Just saw this discussed on NasaSpaceFlight.com:

Untested Rocket Boosts SpaceX Revenue Nearly $1 Billion.
By Amy Svitak
Source: Aviation Week & Space Technology
September 17, 2012

...Another change, she says, involves the rocket's nine Merlin 1D engines, which will be positioned in an octagonal configuration, rather than the “tic-tac-toe” placement on the current Falcon 9.
“You actually want the engines around the perimeter at the tank, otherwise you are carrying that load from those engines that are not on the skin,” she says. “You've got to carry them out to the skin, because that is the primary load path for the launch vehicle."
http://www.aviationweek.com/Article.aspx?id=/article-xml/AW_09_17_2012_p40-495349.xml&p=2

See this thread on NasaSpaceflight for how this engine arrangement might look:

SpaceX Falcon 9 v1.1.
http://forum.nasaspaceflight.com/index.php?topic=28882.msg956757#msg956757

This could have another advantage in that the octagonal arrangement of the engines makes possible the use of an aerospike in the center, if the center engine is removed.
This would give the first stage engines Merlin Vacuum type performance, raising the Isp from the ca. 311 s of the Merlin 1D to the ca. 340 s of the Merlin Vacuum.
This would result in a marked improvement in payload.


Bob Clark

 

[Urwumpe]

Yes, makes sense what is described there... you can actually already calculate this by using graphical computation methods. :lol:

The problem is, that such a placement is not without problems as well.

And no, I know I am the usual fun stopper here, but you won't get vacuum performance by installing an aerospike in the center of a ring of otherwise normal rocket engines. This is not how it works. even the theory of the "boat tail effect" is pretty doubtful today. And an Aerospike engine will also not operate at vacuum performance... it will simply be more effective than other engines outside the design pressure. That does not make it the magical solution for everything.

 

[T.Neo]

Interesting news. I wonder what the manugfacturing/assembly trade-off between this and the 'square' configuration is.

 

[Urwumpe]

Interesting news. I wonder what the manugfacturing/assembly trade-off between this and the 'square' configuration is.

Well the main problem is quite easy to see there: you need a wider stage for fitting 8 engines into a geometry, that has them only on the circumference, compared to alternatives that have center engines or multiple concentric rings (topographically, rings and rectangles are the same... of course not geometrically).

Next, you still need some serious amount of thrust structure - while the construction works great if you have fixed engines thrusting forward, the situation looks differently when the engines gimbal. The radial forces of such a situation have again to be transported evenly on the tank walls, the thrust structure has to withstand it. you also can't just leave the bottom of the tank unsupported, it would simply drop out if the acceleration reaches a critical limit - the lightest way to prevent this is installing a supporting structure below it or go the egg way and have a dome that distributes the loads of the fuel to the side walls. But this would then mean that the tank gets longer and usually heavier, only in very few situations, such a construction works to your advantage (The German 206 series of submarines have such a inverted front bulkhead on their pressure hull)

Structural mechanics are for a very good reason a science of their own... the choices are literally endless and you can never run out of configurations to research, material combinations to test on old structures or simply have to include dynamic behavior better into your tests.

 

[RGClark]

Nice article here:

New Mexico space museum volunteers restoring DC-X for exhibit.
by TopSpacer on February 13, 2013 at 3:01 am
http://hobbyspace.com/Blog/?p=591#comment-7550

Bob Clark

 

[RGClark]

Orbital Science's Antares rocket is scheduled to launch this month:

Orbital's Antares Rocket Rolls Out to Pad in Preparation for First COTS Mission
By Mark Usciak

Antares has a two-day window in which to launch Antares; it stretches from April 17-19. NASA hopes that initiatives like COTS and CRS will enable private companies to handle sending cargo (and perhaps one day crew) to destinations in low-Earth orbit. If these companies can do so affordably, then NASA would be able to conduct operations beyond the orbit of Earth for the first time in more than four decades.
http://www.americaspace.com/?p=33849

This is an important launch to give further support to NASA's more commercial approach to developing launchers.
Another reason this launch is important is because it uses the high efficiency Aerojet AJ-26 engine. This is derived from the Russian NK-33 engine. The NK-33 has long been a favorite of SSTO advocates because of its high Isp and high thrust/weight ratio at the same time.
Ed Kyle's page on the Antares estimates its first stage propellant load as 242 mT, and dry mass as 18.8 mT. The first stage is not weight optimized being based on old 1960's era Russian design.
However, SpaceX has shown by using various weight saving methods such aluminum-lithium alloy and common bulkhead design, that you can get a 20 to 1 mass ratio. Suppose we upgraded the first stage to get a 20 to 1 mass ratio. This would put its dry mass at 12 mT.
Kyle's page gives the AJ-26 a vacuum Isp of 331 s. The twin engines used on the first stage are given a vacuum thrust of 334,000 kgf at 100% and 370,000 kgf at 108%. Orbital Science's Antares brochure gives the vacuum thrust as 3,630 kN, which corresponds to 370,000 kgf, so I'll take this as the vacuum thrust:

Antares™
Medium-Class Launch Vehicle.
http://www.orbital.com/NewsInfo/Publications/Antares_Brochure.pdf

Now use Dr. John Schilling's rocket performance estimation program:

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

Input these numbers for the dry mass, propellant mass, Isp and thrust. Select "No" for the "Restartable Upper Stage?" option. Select Cape Canaveral as the launch site, which will provide for better payload than from Wallops. Input 28.5 degrees as the inclination of the orbit to match the latitude of a launch from Cape Canaveral. Then I get about 3,400 kg to LEO:

====================================
Mission Performance:
Launch Vehicle: User-Defined Launch Vehicle
Launch Site: Cape Canaveral / KSC
Destination Orbit: 185 x 185 km, 28 deg
Estimated Payload: 3399 kg
95% Confidence Interval: 722 - 6633 kg
====================================


Bob Clark

 

[RGClark]

Boeing research on composite hydrogen tanks:

NASA Sees Potential In Composite Cryotank.
By Frank Morring, Jr.
http://www.aviationweek.com/Article.aspx?id=/article-xml/awx_07_01_2013_p0-592975.xml

A key factor in the failure of the composite tanks on the X-33 was their conformal shape. This meant they followed the unusual, non-cylindrical shape of the lifting body itself. Composite LH2 tanks had already been demonstrated with the DC-X program. These however were cylindrical tanks. Lockheed found it difficult to make the conformal tanks on the X-33 composite while maintaining their lightweight.

In regards to the reusable SSTO question though, it doesn't have to be a lifting body. It could be cylindrically shaped using powered descent as SpaceX is planning with the separate stages of a reusable Falcon 9, or by adding wings to the cylindrical rocket body, a la the X-37b.

To this last, it is notable Boeing makes the X-37b, and is doing this research on composite tanks. Also notable is that about the X-37b, Boeing said it is investigating using it as a model for a SSTO stemming from their knowledge of composites:

Boeing proposes SSTO system for AF RBS program.
11 Jun 2011, 15:47 UTC
http://www.portaltotheuniverse.org/blogs/posts/view/121527


Bob Clark

 

[RGClark]

Though in the first test flight of the new version of the Falcon 9, the F9 v1.1, they did not stably "land" the first stage, SpaceX is optimistic they can solve the problem to get a reusable first stage:

SpaceX Hit Huge Reusable Rocket Milestone with Falcon 9 Test Flight (Video)
By Mike Wall, Senior Writer | October 17, 2013 02:01pm ET
http://www.space.com/23230-spacex-falcon9-reusable-rocket-milestone.html

SpaceX also plans to transition the half-scale Grasshopper VTVL test vehicle to a full scale Falcon 9 first stage:

Final flight of Grasshopper v1.0 sets new record.
By Brian Dodson
October 14, 2013
http://www.gizmag.com/grasshopper-retires-altitude-record/29384/

This article says this "Grasshopper 2", as it were, would have all 9 engines of the regular F9 first stage. However, discussions on other forums have said it would only have 3 engines. That would make sense since on stage return, you are using at most 3 engines, and moreover this way, you would not be risking an expensive loss of 9 copies of the Merlins during these Grasshopper test flights.
Still, in point of fact there would be an advantage of using all 9 engines on this first stage Grasshopper, and with a full propellant load. In November, 2012 Elon Musk gave a lecture in London at the Royal Aeronautical Society.

About 30 minutes in, he gave the propellant fraction of the new Falcon 9 v1.1 as around 96%, or perhaps 95.5%. The 96% propellant fraction number gives a 25 to 1 mass ratio. But at an Isp of 311 s for the Merlin 1D, the rocket equation gives a delta-v of 311*9.81ln(25) = 9,800 m/s. Since the delta-v to orbit is only about 9,100 m/s, this would allow a significant amount of payload.
Then using the 9 engines and the full propellant load on the F9 first stage would allow in fact not just a VTVL test vehicle, but in fact a fully reusable and fully orbital vehicle.
Amusingly, about 36 minutes into Elon's lecture someone asks a question about what he sees as the next big breakthrough in rockets after full reusability. Elon thinks for awhile and can't come up with an answer. He finally jokes maybe warp drive. Ironically, he already has the next big advance: a reusable SSTO.

Bob Clark

 

[T.Neo]

Assuming a stage mass of 415 tons, a propellant fraction of 95.5% and a dV to orbit of 9100 m/s, that would be a 'significant payload' of roughly two tons. This with a takeoff mass of over 400 tons; indeed, the majority of F9 v 1.1's takeoff mass, for only a small fraction of the payload. Even Antares lifts more payload, at roughly half the takeoff mass.

It really puts the advantages of staging in perspective; for only about 20% increase in mass, you get an over five-fold increase in payload. And if the first stage truly is the majority of the launch cost, you won't get much of an increase in cost either.

If SSTO were as advantageous, and as possible to make happen with SpaceX hardware, as you make it out to be, then SpaceX would be actively pursuing SSTO vehicles. All indications are that they aren't. It doesn't make sense.

And being able to recover a stage from F9 staging velocity and from orbit are two very, very different things. If you tried that with the F9 first stage, you would end up adding a lot of mass to the stage- obliterating your payload and probably the ability to make orbit altogether.

You also wouldn't be able to deliver payloads to higher orbits, which is a big part of the launch market.

 

[Urwumpe]

Also, the specific impulse at the phase, where most of the fuel is consumed, is 2,730 Ns/kg - and then you suddenly get just 8,787 m/s total DV for the SSTO - without ANY payload.

And the DV to Orbit is not 9100 m/s for normal launch vehicles. It is already pretty optimistic with 9200 m/s which assumes equatorial launch site and no plane changes necessary. The 9100 m/s figure that RGClark constantly uses assumed that the rocket reaches orbital speed in less than 3 minutes - it was a calculation for using the Trident II SLBM for placing a small satellite into Orbit.

 

[RGClark]

Dr. John Schilling's Launch Performance Calculator gives a more accurate estimate of the payload to orbit. SpaceX hasn't released the dry and propellant mass for the F9 v1.1 yet. But taking Neo's 389,000 kg estimate as the propellant load, then a 96% propellant fraction corresponds to a 16,200 kg dry mass.
The total vacuum thrust of the F9 v1.1 is given as 6,672 kN on the SpaceX page. The Merlin 1D vacuum Isp is not given there but it has been reported to be 311 s. Enter these values into the Schilling calculator. Use the default altitude of 185 km, and choose Cape Canaveral for the launch site, at a 28.5 degree inclination of the launch to match the launch site latitude. Note, also select "no" for the "Restartable Upper Stage" option, otherwise the payload will be reduced.
Then the Schilling calculator gives 5,106 kg as the estimated payload:

===================================
Mission Performance: Launch Vehicle: User-Defined Launch Vehicle
Launch Site: Cape Canaveral / KSC
Destination Orbit: 185 x 185 km, 28 deg
Estimated Payload: 5106 kg
95% Confidence Interval: 1170 - 9902 kg
===================================

Note this is actually higher than what you would estimate using a 9,100 m/s required delta-v to orbit. Or said another way, plugging in this payload, and the dry mass and propellant mass numbers into the rocket equation, the delta-v calculates out to be a little less than 9,100 m/s.

If you take the propellant fraction as 95.5%, then the payload is about 3,000 kg. There would clearly be more payloads at the 5,000 kg number, than at 3,000 kg. But it could be profitable to offer launches at the 3,000 kg value, if that's the actual payload for the SSTO. The benefit of the SSTO would be for smaller payloads where the upper stage is not needed.
Why pay $54 million, for wasted payload capability, when you only need the $40 million single stage launcher?


Bob Clark

Correction: that 389,000 kg propellant load number is coming from Ed Kyle's page on the F9 v1.1. This is an estimate and he does not use the 96% to 95.5% propellant fraction estimate of Elon.