Q&A: Pegasus Designer Dr. Antonio Elias

• #220 by yinzer on 11 Sep, 2007 05:57
• I'm intrigued by the idea of what one might be able to do with only one NK-33 on the first stage.  For the second stage, use something similar to the first stage of the IUS.  If you load it up to a liftoff T/W of 1.15, you might be able to get 7500 pounds to LEO.
  
  While this isn't as much as a Delta 792x it's a bit more than the Delta 73/4xx, and those composed a full third of the non-GPS Delta II manifest since 2000.  Giving the 79xx market to the EELVs, this still leaves you a couple flights a year.  At that rate, you can just use the ones that are in the US until they're gone and then decide whether to figure out how to produce some more or to call it a day and count your money.
  
  You could look at offloading a bit of propellant from the first stage and then sticking a Centaur on top to get back to Delta II-level payload, but I'd have to question whether the hassle of doing so (ground handling, etc) is really worth it.  Using a solid second stage seems to open the door to much simpler Minotaur/Taurus style ground processing, while a liquid second stage requires more complex and probably fixed umbilical towers and such.
• #221 by antonioe on 11 Sep, 2007 05:58

• I agree - it sounds very, VERY sensible.  A drawback is that in the absence of a suitable restartable second stage engine (liquid), the use of a solid requires a "super-HAPS" of some kind to match the Delta II payload vs. altitude trade line.  SO now you are talking of THREE stages.  The redeeming fact is that you could get by with a much lower thrust (therefore, small engine(s)) than a true upper stage, so it's really a "quasi-stage" ("vestigial stage"?)

  Another price to pay is that now you have a configuration with all three classical combinations: LOX/Kerosene for S1, a heavy S2 (although not as heavy as, say, a Castor 120), and a "vestigial" S3 with a few thousand lbs of pressure-fed  bi-propellant in it (pressure fed is OK as long as you are in a vacuum and do not require large amounts of thrust), relatively good Isp; in other words, a souped-up GeoCom Apogee propulsion system!

  The solid S2 has the drawback of being perhaps the heaviest item in the stack, and that will drive the size and capabilities of the launch pad ground support equipment.  On the other hand, a bi-prop with a few thousand lbs of propellant could probably be handled just like a large spacecraft, i.e. very limited pad support required.  Remember, when you are launching just a few units a year, the cost of building and maintaining the ground support equipment becomes quite significant!

• #222 by antonioe on 11 Sep, 2007 06:08

• Quote

  Skyrocket - 7/9/2007 7:23 AM 

   Just a little bit of nitpicking: Perseus was not the rider of Pegasus in greek mythology (that imagination was created much later by renaissance artists). In greek mythology the rider of Pegasus was Bellerophon. But in a way Perseus created Pegasus, as Pegasus was born from the blood of the Medusa, which was beheaded by Perseus.

  Right you are!  The name Pegasus, by the way, comes from the greek word for "stream" (Πεγε, I may be missing an accent somewhere), having something to do with the winged horse being sent by Zeus to kick some sense into a presumptuous mountain that wanted to grow up to Zeus' height, causing a stream to flow from where the hoofs hit it (I think this comes from Herodotus).

  I am desperately looking for a copy of a "technical memo"  :laugh:  that I wrote in late 1989 explaining to DWT the minute details of the various Pegasus legends... rats, where did I put it?

  In the meanwhile, here's a Pegasus Trivial Pursuit question than only an European may be able to answer: what is the connection between the Pegasus air-launched rocket, and engine that powered the majority of the airplanes used by the allies in WW I (a.k.a.  "The European War", 1914-1918)___

• #223 by yinzer on 11 Sep, 2007 06:13
• One thing that may be of interest or inspiration when considering ground handling is Curtiss-Wright's RAST system.  It's used to help land helicopters on ships in bad sea conditions; a cable is lowered, a guy runs out and grabs it and attaches it to a winch, and the helicopter is then slowly pulled down to the deck.  Something similar might buy you a couple extra m/s of allowable wind during stacking.
• #224 by antonioe on 11 Sep, 2007 11:34
• Uhhh... I don't quite get it... could you elaborate?  Tnx.
• #225 by A_M_Swallow on 11 Sep, 2007 19:16
• Quote

  antonioe - 3/9/2007  11:34 PM
  

  DWT calls it "Taurus II" but we are feverishly searching for a name (hey, guys, any ideas?)  Some pundits claim that since we're trying to continue the Delta tradition, it shuld be named after the next letter in the Greek alphabet... not a good choice, unfortunately.

  
  Name that follows D for a sexy round object that lifts, hmm - Double D      
• #226 by meiza on 11 Sep, 2007 23:50
• Is any RS-27 variant from Delta II still manufactured / how is the tooling? It's about 900 kN. You'd need quite many of them on the first stage if you avoided solids... But still not as many as Merlin-1C:s, 400 kN.
  In Europe there is no hydrocarbon engine, neither in China, India or Japan. Russians have the RD-180 but that is quite big, 4000 kN... Or then you'd use a solid upper stage with that. You're not planning an SSTO now are you?
  Then there are the hydrocarbon engines used for Soyuz. Interesting. They should be quite damn cheap, although have low ISP. Broadly similar to the RS-27, about 900 kN again. You could use three, two booster RD-117:s and one sustainer RD-118. That'd be a bit like a half-Soyuz, a three-fifths to count properly. It should be light empty, and parallel staging reduces height, meaning possibly easier access to payload. Hmm. There are many Russian upper stage engines to pick from or you could use something else like Kestrels or a Merlin.
  On the other hand, the footprint is big and the integration might be tedious otherwise too, and you'd have to balance engine thrust carefully.
  
  (The NK-33 was 1500 kN.)
• #227 by Jim on 12 Sep, 2007 00:09
• Quote

  meiza - 11/9/2007  7:50 PM
  
  Is any RS-27 variant from Delta II still manufactured
  

  
  Nope, production is done
• #228 by maskims on 12 Sep, 2007 11:29
• Quote

  simonbp - 7/9/2007  2:05 AM
  
  how about Perseus? Rider of Pegasus, slayer of Medusa, and not the name of any rocket I know of...
  
  Simon

  
  If I may, PERSEUS is the name of a French nano launcher project, to be developped mainly through student work. At the rate it's going I doubt it'll fly before tetris/megatron/you-name-it, but having worked on it, I felt obligated to mention its existence !
  
  http://www.cnes.fr/web/3982-perseus.php
  (in French)
• #229 by pippin on 12 Sep, 2007 11:38
• On names: Why always mythology and ships.
  How about just names, "Angelina", for example, sounds nice.
  If you choose a womans' name, typically a lot of songs will be available for promotion as well ;-)
  If your doing BDB, you could also name it "George" or something.
• #230 by edkyle99 on 12 Sep, 2007 17:08
• Quote

  antonioe - 11/9/2007  12:58 AM
  
  

  I agree - it sounds very, VERY sensible.  A drawback is that in the absence of a suitable restartable second stage engine (liquid), the use of a solid requires a "super-HAPS" of some kind to match the Delta II payload vs. altitude trade line.  SO now you are talking of THREE stages.  The redeeming fact is that you could get by with a much lower thrust (therefore, small engine(s)) than a true upper stage, so it's really a "quasi-stage" ("vestigial stage"?)

  Another price to pay is that now you have a configuration with all three classical combinations: LOX/Kerosene for S1, a heavy S2 (although not as heavy as, say, a Castor 120), and a "vestigial" S3 with a few thousand lbs of pressure-fed  bi-propellant in it (pressure fed is OK as long as you are in a vacuum and do not require large amounts of thrust), relatively good Isp; in other words, a souped-up GeoCom Apogee propulsion system!

  The solid S2 has the drawback of being perhaps the heaviest item in the stack, and that will drive the size and capabilities of the launch pad ground support equipment.  On the other hand, a bi-prop with a few thousand lbs of propellant could probably be handled just like a large spacecraft, i.e. very limited pad support required.  Remember, when you are launching just a few units a year, the cost of building and maintaining the ground support equipment becomes quite significant!

  
  After looking at this a bit more, it does appear that two NK-33 engines would be enough for both LEO and GTO missions.  This creates a launch vehicle that could have a liftoff mass, including payload, of as much as 260 tonnes if the minimum Atlas V thrust-to-weight ratio were allowable on liftoff.  
  
  Various upper stage combinations are possible, but a third stage appears necessary for GTO missions regardless of second stage type, unless liquid hydrogen were in the picture.  A mini-Castor 120 (maybe 38 tonnes gross) with a bipropellant pressure fed  third stage (4 or 5 tonnes gross) would be able to do LEO and GTO missions.  
  
  I'm pretty sure, too, that it might be possible to work out  an all-solid motor upper stage combination, using Pegasus upper stages, but I can see how this could be a much less flexible design than one that uses a restartable upper stage.  Much cheaper development though, and would be able to use existing Taurus/Pegasus/Minotaur assets.  
  
  An all liquid design would also need three stages unless liquid hydrogen were in the cards.  Something like a Merlin 1C with a nozzle extension looks, on paper, like the ideal non-hydrogen liquid second stage engine.  A two-stage design with a Merlin 1C second stage can almost, but not quite as near as I can determine, get 1.84 tonnes to GTO.  
  
  SpaceX probably isn't selling Merlins, though!  But where else could one find a 50 tonne thrust second stage bipropellant engine?    
  
  
  BUT THERE IS ANOTHER WAY, and it just now occurred to me - a real "OMYGOSH" moment.
  
  
  Lets go ahead and use that liquid hydrogen upper stage.  RL10 are in production for two other U.S. launch vehicle programs, which promises to minimize engine development and production cost.  Put one of those terrific engines on our second stage.  The stage itself will obviously cost a chunk of change, but so would any bipropellant liquid upper stage.
  
  Suddenly, the gross liftoff mass of our launch vehicle plummets, massively.  Now we need ONLY ONE NK-33 on a first stage topped by only ONE upper stage.  We've doubled the lifetime of the available NK-33 inventory.  Perhaps it won't be necessary to build new ones, since those already built might last for a decade or more!  This machine would be able to trump Delta II big time.  It could weigh less than 120 tonnes at liftoff - only roughly half the liftoff mass of a Delta 7920/25.  It would be a real lightweight on the ground, weighing perhaps less than 8 tonnes dry for the two stages (less than half the dry weight of an Atlas V and many times less mass to erect at the launch pad than with Delta II).        
  
  All manner of possibilities.
  
   - Ed Kyle
• #231 by Nate_Trost on 12 Sep, 2007 18:01
• Wouldn't adding LH2 to the mix increase the cost of the ground infrastructure?
  
  In regard to an upper-stage Merlin, why wouldn't SpaceX want to sell engines for a vehicle that isn't a direct competitor to their line up? More flight heritage on the engines only helps them.
• #232 by edkyle99 on 12 Sep, 2007 18:15
• Quote

  Nate_Trost - 12/9/2007  1:01 PM
  
  Wouldn't adding LH2 to the mix increase the cost of the ground infrastructure?
  

  
  Yes, but in return the first stage propulsion cost (and gross liftoff weight - another cost indicator) would be halved, a return that would accrue with each launch.  I suspect that the savings would quickly pay for the extra ground infrastructure.
  
  

  Quote

  In regard to an upper-stage Merlin, why wouldn't SpaceX want to sell engines for a vehicle that isn't a direct competitor to their line up? More flight heritage on the engines only helps them.

  
  I agree, partly because I think that Merlin is the only sale-able product that SpaceX might ultimately end up with.
  
  But the truth is that this NK-33/RL10 launch vehicle that I described, and the other "Taurus II" ideas, might actually nip at the heels of the basic two-stage Falcon 9 capabilities - not the capabilities that SpaceX has published but the real ones that appear when you sit down with the rocket equation for a few minutes.
  
   - Ed Kyle
• #233 by bobthemonkey on 12 Sep, 2007 18:19
• Answer to the trivia question (I think). The WW1 aircraft used RR engines, as does the the Tristar which carries Pegasus.
• #234 by Seer on 12 Sep, 2007 18:54
• Quote

  edkyle99 - 12/9/2007  1:15 PM
  
  

  Quote

  Nate_Trost - 12/9/2007  1:01 PM
  
  Wouldn't adding LH2 to the mix increase the cost of the ground infrastructure?
  

  
  Yes, but in return the first stage propulsion cost (and gross liftoff weight - another cost indicator) would be halved, a return that would accrue with each launch.  I suspect that the savings would quickly pay for the extra ground infrastructure.
  
  

  Quote

  In regard to an upper-stage Merlin, why wouldn't SpaceX want to sell engines for a vehicle that isn't a direct competitor to their line up? More flight heritage on the engines only helps them.

  
  I agree, partly because I think that Merlin is the only sale-able product that SpaceX might ultimately end up with.
  
  But the truth is that this NK-33/RL10 launch vehicle that I described, and the other "Taurus II" ideas, might actually nip at the heels of the basic two-stage Falcon 9 capabilities - not the capabilities that SpaceX has published but the real ones that appear when you sit down with the rocket equation for a few minutes.
  
   - Ed Kyle

  
  I've wondered about the payload projection for the falcon 9, as well. It's higher than the payload fraction of the Atlas 5, even though the Atlas has a hydrogen upperstage. On the other hand the merlin is a more efficient first stage engine than the equivalant on the Atlas.
• #235 by edkyle99 on 12 Sep, 2007 19:14
• Quote

  Seer - 12/9/2007  1:54 PM
  
  I've wondered about the payload projection for the falcon 9, as well. It's higher than the payload fraction of the Atlas 5, even though the Atlas has a hydrogen upperstage. On the other hand the merlin is a more efficient first stage engine than the equivalant on the Atlas.

  
  Merlin might be ever so slightly more efficient than the old Rocketdyne MA-5A Atlas engines, but it is not anywhere close to being as efficient as the current Atlas V RD-180 engine.
  
   - Ed Kyle
• #236 by tnphysics on 12 Sep, 2007 20:05
• Quote

  Seer - 12/9/2007  2:54 PM

  Quote

  edkyle99 - 12/9/2007  1:15 PM

  Quote

  Nate_Trost - 12/9/2007  1:01 PMWouldn't adding LH2 to the mix increase the cost of the ground infrastructure?

  Yes, but in return the first stage propulsion cost (and gross liftoff weight - another cost indicator) would be halved, a return that would accrue with each launch.  I suspect that the savings would quickly pay for the extra ground infrastructure.

  Quote

  In regard to an upper-stage Merlin, why wouldn't SpaceX want to sell engines for a vehicle that isn't a direct competitor to their line up? More flight heritage on the engines only helps them.

  I agree, partly because I think that Merlin is the only sale-able product that SpaceX might ultimately end up with.But the truth is that this NK-33/RL10 launch vehicle that I described, and the other "Taurus II" ideas, might actually nip at the heels of the basic two-stage Falcon 9 capabilities - not the capabilities that SpaceX has published but the real ones that appear when you sit down with the rocket equation for a few minutes. - Ed Kyle

  I've wondered about the payload projection for the falcon 9, as well. It's higher than the payload fraction of the Atlas 5, even though the Atlas has a hydrogen upperstage. On the other hand the merlin is a more efficient first stage engine than the equivalant on the Atlas.

  The reason is that the Falcon 9 upper stage is so much larger that the first stage dry mass is negligible in comparison. This puts it much closer to the optimum delta-V split. On the other hand, the delta-V split of the Atlas V is skewed towards the first stage doing too much work. The CCB is almost as heavy as the Centaur.
• #237 by Seer on 12 Sep, 2007 21:45
• Yes, my mistake on the merlin engine compared to the rd-180.
   Why was the delta v split between the stages chosen that way?
  I also noticed that the delta 4 payload fraction is similar to the falcon 9, despite both stages being hydrogen on the delta 4. Is the poor performance because of the same reason as on the Atlas?
   I'd thought that having a large upperstage would be a problem for gto payloads, so how can the Falcon 9 have such a large payload (as large as the Atlas 5) to gto? One has to optimise for one or the other, right? Afterall, you can't have your cake and eat it.
  
  
• #238 by Chris Bergin on 12 Sep, 2007 22:13
• Remember, this is the Q&A: Pegasus Designer Dr. Antonio Elias thread, so let's not take it off track from actual questions.
• #239 by antonioe on 13 Sep, 2007 00:02

• Quote

  edkyle99 - 12/9/2007 12:08 PM

  THERE IS ANOTHER WAY, and it just now occurred to me - a real "OMYGOSH" moment. Lets go ahead and use that liquid hydrogen upper stage. RL10 are in production for two other U.S. launch vehicle programs, which promises to minimize engine development and production cost. Put one of those terrific engines on our second stage. The stage itself will obviously cost a chunk of change, but so would any bipropellant liquid upper stage. Suddenly, the gross liftoff mass of our launch vehicle plummets, massively. Now we need ONLY ONE NK-33 on a first stage topped by only ONE upper stage. We've doubled the lifetime of the available NK-33 inventory. Perhaps it won't be necessary to build new ones, since those already built might last for a decade or more! This machine would be able to trump Delta II big time. It could weigh less than 120 tonnes at liftoff - only roughly half the liftoff mass of a Delta 7920/25. It would be a real lightweight on the ground, weighing perhaps less than 8 tonnes dry for the two stages (less than half the dry weight of an Atlas V and many times less mass to erect at the launch pad than with Delta II). All manner of possibilities. - Ed Kyle

  Congratulations! - You've almost described my preferred configuration for Taurus II.  Unfortunately, there are other factors that prevent me from convincing my colleagues of that config... who know, I have until Dec. 5 to change their mind...