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Conspiracy alert!

Was Google able to come up with this doodle so quickly in less than a day or were they clued in beforehand?

  Bob Clark  ;-)

Further about the allowing air into the nozzle to burn with fuel idea: suppose our nozzle is an aerospike. Since it is already open to the air there would be no need to have opening vents on the nozzle.
But by combusting with fuel, we would get a high pressure increase so there is a question if the exhaust gases would still follow the slope of the spike or balloon out. I'm thinking the exhaust gases from the regular combustion chamber would be flowing down at high speed so they would have an effective low pressure. Then if we only added enough fuel to increase to total pressure after the external combustion to sea level level ambient, then the ambient air could still constrain the combustion.

  Bob Clark

GW, that DARPA proposal I wrote was not successful. It was the one we were discussing about new methods of thermal protection in 2013 here:

Index » Interplanetary transportation » Reusable Rockets to Orbit.
2013-10-10 16:47:00
http://newmars.com/forums/viewtopic.php … 19#p117119

This discussion was from 2013. I finally got around to writing the proposal in 2015.

However, what DARPA really wants now in regards to launch access is low cost flights for small payloads, possibly using a reusable booster. The thermal protection issue was not key to that. But what is still a key question and what doomed the X-33 was the inability to get lightweight conformal tanks.

I took a look again at your blog post:

Sunday, October 6, 2013
Building Conformal Propellant Tanks, Etc.

http://exrocketman.blogspot.com/2013/10 … s-etc.html

I'm still struck by your statement that you can get close to the same weight efficiency for lobed tanks as for cylindrical ones using metal tanks. You mentioned the figure of merit that determines the weight growth is perimeter to length. I had suggested that DARPA look again at the X-33 to fill the role of their desired reusable first stage booster:

Saturday, October 5, 2013
DARPA's Spaceplane: an X-33 version.
http://exoscientist.blogspot.com/2013/1 … rsion.html

Looking at pictures of the X-33's lobed tanks, it does look like the perimeter to length ratio would be low, so you could get close to the usual cylindrical tank weight efficiency:

LOCKHEED MARTIN X-33 COMPOSITE TANK TESTING, HYDROGEN TANK MULTI-LOBED AT K SITE, NASA PLUM BROOK STATION.

If you could provide data that support the validity of your perimeter to length ratio figure of merit or even prove it on a small test tank, you might get funding for this.
Note it's not just DARPA that would need this. The Air Force would also need such weight efficient tanks for their hypersonic vehicles which also have a flat rather than round cross-section:

The HTV-3X Hypersonic Test Vehicle.

Bob Clark

Another method to increase thrust at sea level is the "thrust augmentation nozzle", TAN. It's sort of like an afterburner for rocket engines. What it does is inject propellant into the nozzle and ignites it to generate additional thrust. See discussion here:

Thrust Augmented Nozzles
Posted on November 12, 2007 by Jonathan Goff

http://selenianboondocks.com/2007/11/th … d-nozzles/

In experiments the researchers were able to increase thrust by up t0 70%.

The researchers also studied theoretically the case of using RP-1 to inject into the nozzle of a hydrolox engine. They were studying how payload could be increased for a SSTO. Remarkably the payload went up by nearly 3 times, from 25,000 lbs to 70,000 lbs using TAN. See Table 1 here:

THRUST AUGMENTED NOZZLE (TAN) the New Paradigm for Booster Rockets (Preprint).
http://www.dtic.mil/cgi-bin/GetTRDoc?AD … tTRDoc.pdf

I'm wondering if we can get even better performance if we bring outside atmospheric air into the nozzle to burn with the fuel rather than the oxidizer. This would increase Isp if it would work.

I'm thinking of a scenario like this:

Rocket motor thrust nozzle with means to direct atmospheric air into the interior of the nozzle.
US 3469787 A.

https://www.google.com/patents/US3469787

We would open up vents on the nozzle to allow air to flow in, then burn it with the fuel. We would have to insure the vents we opened were further down on the nozzle so that the reduced pressure of the exhaust flow further down would allow the atmospheric air to enter in. We also don't want after we ignite the fuel with the air for this exhaust to exit back out the vents, further reason for making the opened vents to be further down the sides of the nozzle.

  Bob Clark

Found this after web search:

/    The Mars Society    /    Technical Task Force    /    Life Support Project     /

http://home.marssociety.org/tech/test/l … rc/s25.htm

Bob Clark

Thanks for that. It reminds me of something I wrote on sci.space.shuttle after the space shuttle Columbia accident. I ended the post with the question: Are lower-level employees always smarter than top-level management?

=====================================================
From: rgrego...@yahoo.com (Robert Clark)
Newsgroups: sci.space.shuttle,sci.space.history,sci.space.policy,sci.astro
Subject: Re: Washington Post: High level NASA request for Columbia imaging
Date: 15 Mar 2003 02:42:03 -0800
Organization: http://groups.google.com/
Lines: 76
Message-ID: <832ea96d.0303150242.669d5239@posting.google.com>

AbelM...@webtv.net wrote in message news:<23378-3E7...@storefull-2173.public.lawson.webtv.net>...
> I feel vindicated now, because this is exactly what I posted,
> immediately after the Shuttle blew up. You wouldn't believe the names
> people called me, everything from "liberal idiot", to "unpatriotic" and
> so on. I had never been called so many names by so many people.
> I was certain then that it is this corporate culture of intimidation
> that Bush has fostered, it is this same culture of intimidation and of
> looking down on subordinates that also led to 9/11.  Four months before
> 9/11, an FBI Agent, Coleen Rowley warned the FBI that Arab terrorists
> were learning to fly planes but not learning how to land them, she found
> this extremely suspicious, but the FBI heads told her to shut up.  So
> she went to the CIA after that, out of sheer frustration, and she was
> reprimanded, her job was threatened after she did that. 4 months later,
> 9/11 happened. 
>
>...

Shuttle Team Sought Satellite Assessment of Liftoff Damage
"He said Lambert Austin, an engineer at Johnson Space Center in
Houston, had asked Ron D. Dittemore, the shuttle program manager, in a
group meeting to obtain satellite images to help gauge the damage. Mr.
Dittemore turned down the request, even though Mr. Austin was also
speaking for several other engineers, the official said.
"Mr. Austin and his colleagues were disappointed, the official said,
especially because they believed Mr. Dittemore did not have the
technical knowledge of imagery to determine whether the images would
have been helpful.'
http://www.nytimes.com/2003/03/13/natio … 3SHUT.html

About the Coleen Rowley 9/11 memo:

How the FBI Blew the Case
The inside story of the FBI whistle-blower who accuses her bosses of
ignoring warnings of 9/11. A reading of her entire memo suggests a
bracing blueprint for change.
"Rowley and her colleagues continued to plead their case. Her memo
rails against but doesn't name a handful of midlevel officials who
"almost inexplicably" blocked "Minneapolis' by now desperate efforts
to obtain a FASA search warrant ... HQ personnel brought up almost
ridiculous questions in their apparent efforts to undermine the
probable cause." One supervisor complained that there might be plenty
of men named Zacarias Moussaoui in France; how did the agents know
this was the same man? (The agents checked the Paris phone books and
found but one Moussaoui.) At another point the field office tried to
bypass their bosses altogether and alert the CIA's Counterterrorism
Center; Rowley says FBI officials chastised the agents for going
behind their backs."
http://www.time.com/time/nation/article … 94,00.html

Copy of the Coleen Rowley memo here:

Coleen Rowley's Memo to FBI Director Robert Mueller
An edited version of the agent's 13-page letter
"5) The fact is that key FBIHQ personnel whose job it was to assist
and coordinate with field division agents on terrorism investigations
and the obtaining and use of FISA searches (and who theoretically were
privy to many more sources of intelligence information than field
division agents), continued to, almost inexplicably,5 throw up
roadblocks and undermine Minneapolis' by-now desperate efforts to
obtain a FISA search warrant, long after the French intelligence
service provided its information and probable cause became clear. HQ
personnel brought up almost ridiculous questions in their apparent
efforts to undermine the probable cause.6 In all of their
conversations and correspondence, HQ personnel never disclosed to the
Minneapolis agents that the Phoenix Division had, only approximately
three weeks earlier, warned of Al Qaeda operatives in flight schools
seeking flight training for terrorist purposes!"
http://www.time.com/time/nation/article … 97,00.html

   Are lower-level employees always smarter than top-level management?

===================================================

         Bob Clark

Those performance numbers sound great for a jet-augmented rocket launcher. The thrust/weight ratio is closer to that of a rocket rather than a jet, where it's typically in the range of 10. The main problem with using jets for low speed, low altitude portion of the flight to orbit was the heavy weight of jets compared to the thrust they put out. But 50 to 1 would be quite good. And a TSFC, the analog for jets to Isp for rockets, that is close to 1.0, similar to that of turbojets, is also excellent. This is typical for jets but far superior to rockets.

Why wasn't it used on rockets?

   Bob Clark

I only heard of "unsteady flows" in the context of detonations, whereas steady flows would be for example what you get from rocket nozzles. How was unsteady flow achieved in the context of a ducted rocket?

  Bob Clark

This idea of "air entrainment" was used to make an easily inflatable sleeping pad:

Amazing Air Pad Inflates in Seconds w/ NO power or pumping.
http://www.youtube.com/watch?v=JydG8Iyr7Kw

Since this is based on the well-known and well-studied Venturi effect it should be calculatable how much extra thrust can be generated by using it:

https://en.wikipedia.org/wiki/Venturi_effect

A key application would be the SLS core stage. It's irritating that we have these high performance engines in the SSME's designed to be reusable, and we would throw four of them away with each SLS flight. But if you look at the specs on the SLS core, it has the delta-v to be SSTO, but it could not lift off from ground with the four SSME engines. But you need only 50% more thrust for it to be able to lift off. Could using a duct ring allow it have the extra thrust needed?

  Bob Clark

I'd like to see this actually be tried. For instance the famous Centaur upper stage, used for example on the Atlas V, has enough delta-v to be SSTO, but it's engine does not have enough thrust to take off from the ground. Also, it already has a nozzle extension attached that is used to increase the area ratio in vacuum. Perhaps this nozzle extension when not extended could act just like ring duct for a ducted rocket.

It would need though to be able to double the thrust for it to work though.

  Bob Clark

You should read the comments to the GW post. The analysis in the post is based on assumptions GW made for the possible Isp and dry mass fraction. Both of these have been exceeded for real world rockets. When you take into account what's actually doable now you find the payload for a SSTO is significantly higher so that you have sufficient payload capacity to add the systems needed for reusability.

  Bob Clark

Yet another idea for an altitude compensating nozzle attachment to existing engine nozzles:

Altitude compensation attachments for standard rocket engines, and applications, Page 3: stretchable metal nozzles.
http://exoscientist.blogspot.com/2016/0 … s-for.html

The altitude compensating nozzle known as the aerospike has been known since the 60's. The problem is it would require the engine to be designed for it from the start, since for one thing it would need a toroidal combustion chamber. A change like this would be an expensive change for an already existing engine, and you might as well just design a new engine from the start.

Therefore I have been investigating ways of getting the altitude compensation just by making an attachment to an already existing engine's nozzle. Here is another method. The idea behind it is that metal becomes much more malleable at high temperatures. Then you would allow this nozzle extension to reach the temperatures where it can be stretched much more easily, but below the melting point, so it is still solid. To effect the nozzle stretch you could either use extensible actuator rods or high pressure gas injected into hollow nozzle walls.

  Bob Clark