Q&A: Pegasus Designer Dr. Antonio Elias

• #80 by antonioe on 08 Oct, 2006 02:46

• Quote

  meiza - 26/9/2006 6:22 AM
  
  One stranger question.
  
  Did you ever think about making the Pegasus first stage reusable? It already has wings, but how does the first stage actually behave now after staging?
  Reusability would have probably meant liquid pressure-fed first stage and launch from a specific site so you can land / ditch it in an appropriate place. But it'd be cheap to operate, just reloading the propellants.

  Yeah, we did once (although not changing it into a liquid, but refilling the case à la Shuttle SRBs); but between the resulting loss in payload (parachutes, flotation gear, reentry tps, etc) and the cost of fishing the stage and refurbishing it, it very, very clearly did NOT pay off.

  We also looked at putting some "simple" (ha!) turbojets in the wing's "armpits" to increase the effective Isp between drop and, say, M=3, and it also did not work out (BTW, that idea came from a respected professor of Aeronautics that shall remain unnamed from a prestigious university that shall remain equally unnamed... Dave Thompson INSISTED that we look into it.  We did, and did not like what we saw; if I get off my #ss and buy a scanner this weekend, I'll scan and post some pictures of that design... looks cool and doesn't work, like many other ideas...).

  Working on the next installment... be patient!!!

• #81 by Chris Bergin on 08 Oct, 2006 17:14
• Quote

  antonioe - 8/10/2006  3:29 AM
  
  Working on the next installment... be patient!!!

  
  Looking forward to it
• #82 by antonioe on 09 Oct, 2006 23:32

• The Pegasus story, Part III A pilgrimage to the desert.

  One of the first decisions we had to make was what size exactly to shoot for: a Scout replacement?  Well, that was the only real small launcher around in mid-1987, with 98 launches in its various forms, from the original "Scout-X" first launched in December 1960 (Ohmygod, I was 11 years old then!) to the then-current, and eventually final configuration, the Scout G-1 (Scout went on to fly 5 more times before the first Pegasus flight, then 6 more after that, with the last Scout - number 109! - on May 9, 1994.  Scout was an amazing rocket, some day I have to write a bit about it!)

  
  At the time, however, we did not want to compete with Scout.  Actually, we thought we could find a niche below the Scout G's 200 or so kg of payload to LEO - therefore the 20klb and 6klb sizes mentioned in "Part II".  So we started looking at what aircraft we could use to launch "it".

  
  "It", by the way, was not called Pegasus.  That name came by later.  I initially called it "SALVO" (Small Air-Launched Vehicle to Orbit"), and somewhere I have a notebook which I called the "Design Binder" countaining the evolving informal baseline.  The "Design Binder" described (again, very informally, but very descriptively) the vehicle, the trajectory, the flight operations (at least conceptually), the ground support equipment (a very important part of the "system"), etc. etc.  It never grew over 15 or 20 pages, and was labeled simply "SALVO Design Binder".  There was exactly ONE copy that we all shared.  The team, however, thought "SALVO" was a little too... baroque?  So we simplified it to "ALV".  And so it was called until Frank Bellinger and I – independently – came up with the name “Pegasus”.

  
  Back to the launch aircraft; I did a quick and dirty trade between launch speed (essentially subsonic and two flavors of supersonic: Mach 2 for an F-15 class aircraft, and Mach 3 for an SR-71) and sheer size.  Almost effortlessly, sheer size won (considerably reducing the anxiety about supersonic separation... we had very much in mind the problems the SR-71 had with the D-21 drone, and had visions of the SR-71 people's reaction to our proposal: "you want to do WHAT!!!...)
  

  We looked first at the C-130, specifically, at the Hercs modified to carry "Firebee"-type UAV's.  Although most of the versions of the venerable Ryan drone family were in the 2,000-4,000 lbs category (four could be carried by a Herc on pylons rated for about 5,000 lbs each), there were, apparently, a couple Hercs with only two 10,000-lb capable pylons.  Paul Hudson sketched it (see below).

  Soon it became apparent that 20,000 lbs was probably the smallest size we would be willing to approach for a very simple reason: the smaller the vehicle, the more sensitive its payload becomes to small errors in, say, structural mass, aerodynamic drag, engine performance, etc.  Years later I attempted to quantify this effect by introducing the notion of "G/P" (ratio of gross mass to payload mass) for a launch vehicle, and a formula that relates G/P to the structural mass fraction s of a stage and the stage's final to initial mass ratio r (itself related to the specific impulse and the DV required - but I digress).
  

  Next to be analyzed was the C-141.  Although C-141s has now been retired, at the time they were very desirable military transports, read hard to get your hands on.  (see Paul's sketch below).

  I've also included two VuGraphs from the 8 September 1987 presentation to the USAF and Aerospace Corporation (more about that day later)  which summarize the aircraft trades; as one of the VuGraphs claim, we had a "verbal agreement" with NASA Dryden that they would support "the first 10 launches".

  
  Sometime in the late spring or early summer of 1987 Bob Lovell, Bob Lindberg and I visited NASA's Dryden Flight Research Center (DFRC) then headed by former first-generation CIA U-2 pilot Marty Knutson ("it could have been me rather than Gary...").  We met with the Director, Flight Operations Engineer Bill Albrecht (the voice of "NASA-1") and somebody else whose name - sorry - I don't remember.  They listened to us very politely and, when we finished out presentation, and much to our amazement, they said: "that sounds like a very interesting idea; would you like to take a look at the aircraft?"  I remember almost passing out - I had half expected to be laughed out of the place.  Instead, Bob Lindberg and I went down to the ramp with Bill Albrecht and proceeded to look at NB-52-008, the second of the two B-52's that the USAF had consigned to NASA for the X-15 program (that's right: 0008 means it was the eight production aircraft... the "older" one, by then mothballed at Davis-Monthan, was S/N 3!!!).

  
  By this time it was the mid-afternoon; we crawled through the rather hot interior of the fuselage and were amazed at how old it looked.  A Sony Trinitron monitor that seemed to belong to somebody's living room was installed at the launch Panel Operator (LPO) station in the back of the top deck of the cabin (more about that monitor in a later chapter).  Yes, the cabin has two decks, but, amazing as it may sound, the fuselage is narrow enough for me to be able to touch both sidewalls with my outstretched arms.  And, oh, yes, we found why B-52 pilots wear helmets: you always bang your head against the edge of the entry hatch getting in.
  Back outside, Bob and I tried to estimate the height between the X-15 pylon and the ground by my standing under it and Bob pacing back to use my (short) height as a rough visual "ruler": "hmm... seems to me about 1.8 Antonios..."  We then started pacing the shadow of the slot cut in the trailing edge of the wing for the X-15 vertical tail when Bill Albrecht took pity on us and produced, seemingly out of nowhere, a small 8 foot measuring tape.  In the excitement of the day I forgot to return the tape to Bill.  Today, nineteen years later, I still have Bill's tape - one of my most prized mementos of those glorious days (Bill, if you ever read this, yes, you can have your tape back...).  I included a picture I just made of that historic artifact.

  
  When Bill told us that he was the guy on the radio that controlled the Dryden missions ("NASA-1") I told him I wanted *BADLY* to be the first Launch Panel Operator (LPO), and that, if I pulled that miracle off, I wanted a deal with him:  If the first flight were to make it to orbit, he was to call me on the radio: "NASA-1 to LPO, Pegasus is in orbit", to which I would reply, using my coolest Tom Wolf "Right Stuff" voice, "uhh... Roger that".
  

  We had our launch aircraft; now, we needed a rocket.

  Next installment: Run silent, run deep.

   

  ---

  

  

  

  

  

  
• #83 by George CA on 10 Oct, 2006 00:30
• This is really interesting and we appreciate the historical value to your reccolations of the early years of this great launch system!
• #84 by Carl G on 10 Oct, 2006 03:14
• Quote

  antonioe - 9/10/2006  6:15 PM
  In the excitement of the day I forgot to return the tape to Bill.  Today, nineteen years later, I still have Bill's tape - one of my most prized mementos of those glorious days (Bill, if you ever read this, yes, you can have your tape back...).  I included a picture I just made of that historic artifact.

  
  These stories are great. Physical items like that tape make it all real (thanks for the picture).
  
  It's hard to imagine that because of how the Pegasus works, but thanks for emphazing the point of needing to get the right carrier aircraft.
• #85 by SRBseparama on 10 Oct, 2006 03:19
• "hmm... seems to me about 1.8 Antonios..."
  
  Was there a time where you thought Pegasus wouldn't get off the drawing board and at what point did that happen?
• #86 by SimonShuttle on 23 Oct, 2006 17:36
• Relevant, and potentially a smile generating release for the good Dr:
  
  http://www.orbital.com/Template.php?Section=News&NavMenuID=32&template=PressReleaseDisplay.php&PressReleaseID=577
• #87 by josh_simonson on 24 Oct, 2006 00:01

• Did you investigate ramjets as well?  They're well suited to being dropped at speed as well as being simpler than turbojets.  I suspect though that pegasus starts to run out of atmosphere soon enough that an air-breathing system wouldn't have much chance to earn it's keep in added cost per added pounds to orbit.
  

   

  >We also looked at putting some "simple" (ha!) turbojets in the wing's "armpits" to increase the effective Isp between drop and, say, M=3, and it also did not work out (BTW, that idea came from a respected professor of Aeronautics that shall remain unnamed from a prestigious university that shall remain equally unnamed... Dave Thompson INSISTED that we look into it.  We did, and did not like what we saw; if I get off my #ss and buy a scanner this weekend, I'll scan and post some pictures of that design... looks cool and doesn't work, like many other ideas...).

• #88 by BFRC on 06 Nov, 2006 02:33
• Antonio,
  
  Why can't the pegasus use the aircraft power for its elevon sweep test at L-5 seconds. It squibs the batteries to perform this test thus forcing a longer turn-around time if the test is unsuccessful (have to swap the batteries out). Seems like you could verify a frozen pin with aircraft power and have a quicker turnaround on the ground.
  
  Second Question: with regard to drag and nozzle control authority, does the wing really help?
  
  
  Thanks
• #89 by antonioe on 07 Nov, 2006 02:55

• (Various throat-clearing sounds...) well... the original purpose of the fin sweep test was to test EVERYTHING associated with the fins, including the thermal battery - not just the pins.  As a matter of fact, the main original purpose of the test was PRECISELY to make sure the thermal batteries didn't have a "false start" (voltage OK but not enough current capacity under load - I can't remember the chemistry of why that could happen).  These are pretty high voltage batteries (about 95 volts, if I remember correctly?)
  
  In reality, they have a humongous margin (battery manufacturers are NOTORIOUSLY conservative in their specs) so we probably could squib them a lot earlier and still have margin. But so far, it has not been worth trying to experiment with that.

  As for your second question, I'm not sure I understand it correctly: the wing does indeed increase drag, but that is a small price to pay for the reduction in gravity losses and the ability to take advantage of the entire forward speed of the carrier aircraft.  I'm not sure what you mean by nozzle control authority.
  
  
  
  

• #90 by antonioe on 07 Nov, 2006 03:01
• Quote

  josh_simonson - 23/10/2006 6:44 PM
  
  

  Did you investigate ramjets as well?.

  
  Same problem as with turbojets: you can design them with a modest efficiency at ONE Mach number, but as soon as you are a little bit slower or a little bit faster, their efficienty goes to pot.  At least, with the turbojet (note: NOT turbofan!!!) you can get decent thrust right after drop, subsonically.
• #91 by antonioe on 07 Nov, 2006 03:28
• Was there a time???!!!  I was running scared ALL the time... that we would run out of money, that the performance would degrade to nothing, that we had made a design mistake, an assembly mistake, that the first stage motor would explode right after ignition... all sort of horrible things went through my mind!  Eeevery day felt like taking a deep breath, closing your eyes and jumping off the 5-meter diving board!
  
  A related question is: was there a point when that feeling disappeared?  Because indeed, there was one (here I'm stealing the thunder from the last installement):  about two weeks before the first flight, I decided to concentrate on flight operations - I had talked my way into begin the first Launch Panel Operator, and true to the test pilots's prayer ("God, please don't let me  f--- up!") I "disconnect" from everything else that was going on around me - even the "Rovner Incident" that I will talk about!  All of sudden I felt a great peace, as if the outcome of the launch was totally unimportant... that sense of detachment lasted through the flight, through the press conference, the party that night, the dunking in the hotel pool... I guess nobody noticed my behavior because they were too excited themselves, but looking backwards I surely must have appeared a bit detached.
  
  I "woke up" three days later when we received the fax from NORAD with the TLE's... all of suddent it hit me that we made it, that there was something in orbit out there that we had made with our own hands... I simply cannot describe the adrenaline rush I got that instant!
  
  
  
• #92 by Jonesy STS on 07 Nov, 2006 19:53
• Brilliant stories! Keep em coming!
• #93 by BFRC on 09 Nov, 2006 03:48
• Sir, thank you for the reply. The purpose of the question regarding control authority with the 1st stage nozzle was to ask if you had enough (without a wing) to overcome the horizontal orientation from aircraft sep. I guess you wouldn't get to take full advantage of the aircraft's forward velocity but the question remains: If you dropped a pegasus (no wing) from the L-1011, could the 1st stage provide enough thrust vectoring to overcome the horizontal orientation . If it could overcome the orientation, how much does the wing actually buy you considering the drag tradeoff?
• #94 by meiza on 09 Nov, 2006 11:08
• bfrc, the whole question has been analyzed in depth in this thread with spreadsheets and all provided.
• #95 by Chris Bergin on 09 Nov, 2006 16:19
• Quote

  antonioe - 7/11/2006  4:11 AM
  
  Was there a time???!!!  I was running scared ALL the time... that we would run out of money, that the performance would degrade to nothing, that we had made a design mistake, an assembly mistake, that the first stage motor would explode right after ignition... all sort of horrible things went through my mind!  Eeevery day felt like taking a deep breath, closing your eyes and jumping off the 5-meter diving board!
  
  A related question is: was there a point when that feeling disappeared?  Because indeed, there was one (here I'm stealing the thunder from the last installement):  about two weeks before the first flight, I decided to concentrate on flight operations - I had talked my way into begin the first Launch Panel Operator, and true to the test pilots's prayer ("God, please don't let me  f--- up!") I "disconnect" from everything else that was going on around me - even the "Rovner Incident" that I will talk about!  All of sudden I felt a great peace, as if the outcome of the launch was totally unimportant... that sense of detachment lasted through the flight, through the press conference, the party that night, the dunking in the hotel pool... I guess nobody noticed my behavior because they were too excited themselves, but looking backwards I surely must have appeared a bit detached.
  
  I "woke up" three days later when we received the fax from NORAD with the TLE's... all of suddent it hit me that we made it, that there was something in orbit out there that we had made with our own hands... I simply cannot describe the adrenaline rush I got that instant!
  
  
  

  
  Heh, that's brilliant.
• #96 by Doug Stanley on 14 Nov, 2006 18:32
• Quote

  Chris Bergin - 9/11/2006  11:02 AM
  
  

  Quote

  antonioe - 7/11/2006  4:11 AM
  
  Was there a time???!!!  I was running scared ALL the time... that we would run out of money, that the performance would degrade to nothing, that we had made a design mistake, an assembly mistake, that the first stage motor would explode right after ignition... all sort of horrible things went through my mind!  Eeevery day felt like taking a deep breath, closing your eyes and jumping off the 5-meter diving board!
  
  A related question is: was there a point when that feeling disappeared?  Because indeed, there was one (here I'm stealing the thunder from the last installement):  about two weeks before the first flight, I decided to concentrate on flight operations - I had talked my way into begin the first Launch Panel Operator, and true to the test pilots's prayer ("God, please don't let me  f--- up!") I "disconnect" from everything else that was going on around me - even the "Rovner Incident" that I will talk about!  All of sudden I felt a great peace, as if the outcome of the launch was totally unimportant... that sense of detachment lasted through the flight, through the press conference, the party that night, the dunking in the hotel pool... I guess nobody noticed my behavior because they were too excited themselves, but looking backwards I surely must have appeared a bit detached.
  
  I "woke up" three days later when we received the fax from NORAD with the TLE's... all of suddent it hit me that we made it, that there was something in orbit out there that we had made with our own hands... I simply cannot describe the adrenaline rush I got that instant!
  
  
  

  
  Heh, that's brilliant.

  
  Now you all know why I decided to abandon my 12 year NASA career one sunny October morning in 1998 to go work for Antonio and Mike Griffin at Orbital...It was worth it for the entertainment value alone!!  
  
  Hi Antonio!
  
  Doug
• #97 by antonioe on 16 Nov, 2006 06:47
• Hi Doug!  I see you have been grilled about the ESAS... did you tell them about your "incident" with Dan G. the day of the X-34 rollout?... you had just finished the CRV Phase I study.... you had a picture of the CRV on top of an EELV (Delta-IV - I still have the original in my office) in an exhibit inside "Stargazer"... Dan G. sees it, hits the ceiling, grabs you by the throat and swears that this country would never, never, ever fly an astronaut on an ELV again and that YOU, Doug Stanley, is doing a GREAT DISSERVICE to NASA and the space program by pushing such a foolish and unsafe idea...
  
  Stanley: 1, Goldin: 0
  
• #98 by Peter NASA on 16 Nov, 2006 15:29
• Quote

  antonioe - 16/11/2006  1:30 AM
  
  Hi Doug!  I see you have been grilled about the ESAS... did you tell them about your "incident" with Dan G. the day of the X-34 rollout?... you had just finished the CRV Phase I study.... you had a picture of the CRV on top of an EELV (Delta-IV - I still have the original in my office) in an exhibit inside "Stargazer"... Dan G. sees it, hits the ceiling, grabs you by the throat and swears that this country would never, never, ever fly an astronaut on an ELV again and that YOU, Doug Stanley, is doing a GREAT DISSERVICE to NASA and the space program by pushing such a foolish and unsafe idea...
  
  Stanley: 1, Goldin: 0
  

  
  Dan Goldin, now that was one scary administrator!
• #99 by vt_hokie on 16 Nov, 2006 18:24
• Speaking of X-34, what ever happened to the vehicle after the program was cancelled?  Unlike X-33, wasn't X-34 more or less ready to fly?