Air launch capability

[halman]

pistolPete,<br /><br />This whole discussion seems off course to me. Launching at supersonic speeds is not going to impart any great advantage, because the whole reason for using a carrier aircraft is not, as one poster put it, to get the space vehicle high enough to increase the efficiency of the rocket engine. The purpose is to get the vehicle above the densest part of the atmosphere so that it can accelerate at full throttle without being torn apart by aeordynamic turbulance. Why does the shuttle throttle the main engines back to 60 percent right after lift off? So that it won't get going too fast in the lower atmosphere. Once the point of max-Q is passed, they can pour the coal on.<br /><br />There is no existing vehicle that I am aware of that will be able to carry an orbital-capable manned spacecraft, unless it is a very small capsule on a solid rocket booster. We need to start from scratch, because the mission requirements of a carrier aircraft are unlike anything that has ever been built. (Except for the White Knight.) You want to have a carrier aircraft whose empty weight is considerably less than the payload it is to carry, but can carry a fuel load which is several times its own weight. You want an aircraft which is a fuel tank shaped into a wing, with many times the amount of thrust that the carrier needs to fly.<br /><br />At some point, the orbiter will get too big to launch under the wing, because the wing has to be distorted to allow for the landing gear to reach the ground with the payload underneath it. By puttitg the payload on the back of the carrier, it is possible to keep the wing in a fairly straight line, so that structural weight is kept to a minimum. An orbiter perched on top of a wing which has no tail section is free to run up its engines to full thrust without crisping the carrier. <div class="Discussion_UserSignature"> The secret to peace of mind is a short attention span. </div>

 

[edkyle98]

"...the whole reason for using a carrier aircraft is not, as one poster put it, to get the space vehicle high enough to increase the efficiency of the rocket engine. The purpose is to get the vehicle above the densest part of the atmosphere so that it can accelerate at full throttle without being torn apart by aeordynamic turbulance."<br /><br />Air launch results in a more efficient launch vehicle (due to higher specific impulse at higher altitudes, a bit less gravity loss, etc.), which means a lighter launch vehicle for the same payload. Less gross launch mass means that the main engine can produce less thrust, which can be a big money-saver - because thrust costs money. <br /><br />An air launch vehicle also flies through a region of maximum dynamic pressure, BTW. <br /><br /> - Ed Kyle<br />

 

[willpittenger]

First, Enterprise did seperate from the SCA several times, including with the SSMEs exposed.<br /><br />However, you would have no fuel for the SSMEs. So you would be stuck with gliding home. <div class="Discussion_UserSignature"> <hr style="margin-top:0.5em;margin-bottom:0.5em" />Will Pittenger<hr style="margin-top:0.5em;margin-bottom:0.5em" />Add this user box to your Wikipedia User Page to show your support for the SDC forums: <div style="margin-left:1em">{{User:Will Pittenger/User Boxes/Space.com Account}}</div> </div>

 

[halman]

edkyle98,<br /><br />Is the region of maximum dynamic pressure for a vehicle launched at 50,000 feet the same as for one launched at sea level? If not, is the region of max Q for an air launched vehicle at an altitude where the air density is so low that the turbulance will not have much effect on the airframe? I have the understanding that excessive velocity in the max Q regieme for a vehicle launched at sea level can result in the air frame breaking up. But over 3/4 of the atmosphere is below you at 50,000 feet. <div class="Discussion_UserSignature"> The secret to peace of mind is a short attention span. </div>

 

[PistolPete]

Halman, the Russian aerospace corporation Molniya (the same people who build the Buran space shuttle), have plans for an aircraft that can do just what you are talking about. It is called the Molniya-1000 Heracles <div class="Discussion_UserSignature"> <p> </p><p><em>So, again we are defeated. This victory belongs to the farmers, not us.</em></p><p><strong>-Kambei Shimada from the movie Seven Samurai</strong></p> </div>

 

[propforce]

<blockquote><font class="small">In reply to:</font><hr /><p>Launching at supersonic speeds is not going to impart any great advantage, because the whole reason for using a carrier aircraft is not, as one poster put it, to get the space vehicle high enough to increase the efficiency of the rocket engine. The purpose is to get the vehicle above the densest part of the atmosphere so that it can accelerate at full throttle without being torn apart by aeordynamic turbulance. ...<p><hr /></p></p></blockquote><br /><br />I have to disagree. Launching (separating the rocket from the carrier aircraft) at supersonic speed imparts a GREATER advantage more so than at a high altitude (the use of high altitude, subsonic aircraft, or a high altitude balloon, for example). <br /><br />Keep in mind that max-Q is a relative number, and it is different for each vehicle. Max-Q is calculated by the ambient pressure (change as a function of altitude) multiplied by the SQUARE of Mach number. So theoretically one can have a greater Max-Q for a air-launch rocket than a ground-launch, if one is so inclined to design for a higher Q flight. <br /><br />The reason why a ground launch vehicle, such as the shuttle, can ONLY withstand a lower Max-Q can be illustrated as follows: Take a pencil in both hands, with one hand on each end. As the vehicle turn into its flight path angle, say 45 degrees, the dynamic pressure (Q) it is being subjected to is like flexing this pencil with your hand bending on both ends. As you can imagine, a forceful bend can break the pencil in half !!! As a minimum, you can feel the pencil flexes, and this adds to difficulties in controling the flight of rocket. <br /><br />Now take the same pencil and place it in a 45 degree position. The same level of dynamic pressure (Q) is only acting on its nose and is being counter by the engine thrust from its end. This is equivalent to using both hands and squeez the pencil from tip to toe. So you are not bending the pencil but rather sq <div class="Discussion_UserSignature"> </div>

 

[barrykirk]

There are other advantages to high altitude launch.<br /><br />If the altitude is high enough, than the Max Q is much much lower and the aero shroud that is usually discarded after leaving the atmosphere can be made thinner and lighter or possibly even left off entirely.

 

[scipt]

... how about air launch.... then a motor section as per the SS1/SS2.. which could provide some alt. and enough velocity.. then have a scramjet kick in to give more velocity?<br /><br />I know that scramjet technology is hardly up to speed yet (pun intended), but would it be an option? Could it help when coupled with the standard SS1/SS2 style motor?<br /><br />Could reusable scramjet boosters which get jettisioned work? <div class="Discussion_UserSignature"> </div>

 

[edkyle98]

"Is the region of maximum dynamic pressure for a vehicle launched at 50,000 feet the same as for one launched at sea level?"<br /><br />Max-Q is unique for every launch vehicle, whether ground or air launched. It depends on air density and velocity. The equation is air density times the square of velocity. An air launched vehicle does avoid the most dense layers of atmosphere, so it should be easier to design for a lower maximum dynamic pressure. If two identical launch vehicles were flown, with one launching from the ground and one being air launched, the air launched vehicle should experience lower Max-Q conditions than the ground launched vehicle.<br /><br /> - Ed Kyle

 

[propforce]

<blockquote><font class="small">In reply to:</font><hr /><p>Max-Q is unique for every launch vehicle, whether ground or air launched. It depends on air density and velocity. The equation is air density times the square of velocity. An air launched vehicle does avoid the most dense layers of atmosphere, so it should be easier to design for a lower maximum dynamic pressure. <p><hr /></p></p></blockquote><br /><br />That's why you should ALWAYS launch in the summer time, that's when the air is less dense than in the winter. <div class="Discussion_UserSignature"> </div>

 

[vulture2]

Air launch is a complex topic. The X-34 was suborbital but would have provided real data and useful experience. We still need a reusable suborbital test vehicle; intial tests can be done with existing carrier aircraft like the OSC L-1011. <br /><br />Various concepts have been proposed for a second level of testing with a small unmanned upper stage that could reach orbit; one DOD concept would use a more or less conventional supersonic carrier aircraft that would make a zoom climb to ~30km and release the upper stage at Mach 2-3. At this altitude dynamic pressure is low and carrying the upper stage under the carrier would simplify separation. <br /><br />But the central point is that we need to get some flight experience with unmanned air-launched systems before we can sensibly design a manned vehicle. Cancellation of the X-34 was, I believe, a serious error.

 

[holmec]

Thus a new type of airplane is comming out. The configuration of WhiteKnight of Scaled Composites. Its the first plane to deal with this problem. And it seems promising that with composites you can build a light wieght plane with huge amounts of lift and strength to wield a rocket and capsule into the sky.<br /><br />I don't think the metal air liners are up for the job. <div class="Discussion_UserSignature"> <p> </p><p><font color="#0000ff"><em>"SCE to AUX" - John Aaron, curiosity pays off</em></font></p> </div>

 

[halman]

propforce,<br /><br />I have to differ with you. I don't think that turning the vehicle has much to do with max Q. If the vehicle were to launch at a 45 degree angle, it would still have to thottle back the same amount after leaving the pad, because the thrust is capable of accelerating the vehicle at a rate where max Q velocity will be reached in a matter of a few seconds near sea level. This is not to say that aeodynamic effects will not be more pronounced during a turn, however.<br /><br />At 50,000 feet, max Q does not occur until velocities well above 3,000 miles per hour.<br /><br />To acheive correct flight angles at ignition, the carrier wing should pull up into about a 30 degree flight angle before relaese. <div class="Discussion_UserSignature"> The secret to peace of mind is a short attention span. </div>

 

[PistolPete]

<blockquote><font class="small">In reply to:</font><hr /><p>Various concepts have been proposed for a second level of testing with a small unmanned upper stage that could reach orbit; one DOD concept would use a more or less conventional supersonic carrier aircraft that would make a zoom climb to ~30km and release the upper stage at Mach 2-3. At this altitude dynamic pressure is low and carrying the upper stage under the carrier would simplify separation.<p><hr /></p></p></blockquote><br />At ~30km (~100,000 ft.) the atmosphere is virtually nonexistant and Max-Q doesn't really come into play. Take for example the fact that at 100,000 ft. aerodynamic flight controlls do not have enough air flowing over them to work so RCS thrusters have to be used. An excellent case study on aerodynamics at ~100,000 ft. can be read in Tom Wolfe's <i>The Right Stuff</i>. Specifically the segment on Chuck Yeager's near-fatal flight in an NF-104.<br /><br />It could be possible for the second stage to be shrouded in an aerodynamic shell that would be jettesoned before igniton, reducing LV weight which would directly transfer to a higher payload.<br /><br />Or perhaps the 2nd stage could fit into an internal bay and be jettesoned beyond ~100,000 ft. <div class="Discussion_UserSignature"> <p> </p><p><em>So, again we are defeated. This victory belongs to the farmers, not us.</em></p><p><strong>-Kambei Shimada from the movie Seven Samurai</strong></p> </div>

 

[PistolPete]

I've got a couple of links for all of you. Both of them deal with DARPAs RASCAL (Rapid Access Small Cargo Affordable Launch) program that was canceled last year.<br /><br />The first is from Space Launch Corp., the winner of the RASCAL contract.<br /><br />The other is from a group called PanAero and it's plan to use the F-14 as a 1st stage in a space launcher. <div class="Discussion_UserSignature"> <p> </p><p><em>So, again we are defeated. This victory belongs to the farmers, not us.</em></p><p><strong>-Kambei Shimada from the movie Seven Samurai</strong></p> </div>

 

[bdewoody]

All you would need to add for high altitude stability would be some reaction control jets like the X-15 had. Air launch still won't get you past the biggest problem, re-entry. <div class="Discussion_UserSignature"> <em><font size="2">Bob DeWoody</font></em> </div>

 

[propforce]

halman,<br /><br />Here's a good link on the aerospaceweb explaining Space Shuttle Max-Q as well as how to calculate. Simply stated, max-Q is a result of a combination of variety of conditions. Most importantly, it has to do with the level at which the vehicle was DESIGNED to withstand. <br /><br />The previous posts stating that [one of] the advantages of air launch is the vehicle will experience a much lower max-Q is simply NOT correct as evidenced by existing launch vehicles today. <br /><br />Here's a summary of some U.S. launch vehicles and its max-Q to-date that I've compiled.<br /><br />Shuttle, max-Q = ~690 at alt = 35K ft & vel = 1,450 fps<br /><br />Pegasus, max-Q = 1,250 at alt = ~38K ft<br /><br />Atlas V, max-Q = 800 at alt = 34~45K ft<br /><br />The data on the shuttle was taken from the link above. Both Pegasus and Atlas V numbers is from Isakowitz, et. al. Note that one explanation could be that the Pegasus uses solid motors therefore would withstand a higher Q with it's beefier motorcase design than other vehicles which are liquid fueled stages. This goes back to my original point on how each vehicle is designed to handle a different max-Q.<br /><br />While the Delta IV max-Q number is not published (I could not find), I can estimate within a reasonable confidence it's in the neighborhood of Atlas V max-Q, except for the DIV-H which is significantly lower. All occur within the same range of altitude. It's too bad that Ariane does not publish it's max-Q number neither. <br /><br />You've mentioned the vehicle acceleration (g's) factor in calculating max-Q. Suprisingly you'll find that vehicle is well within its acceleration (g's) limit while the max-Q occurs. For example, Delta IV's max-Q occurs at 1.4 ~ 1.7g while it's maximum g-acceleration is around 5. Therefore, the g-limit is not a factor in determining max-Q.<br /><br />Also, although the Shuttle pitch over v <div class="Discussion_UserSignature"> </div>

 

[propforce]

<blockquote><font class="small">In reply to:</font><hr /><p>That's why you should ALWAYS launch in the summer time, that's when the air is less dense than in the winter. <p><hr /></p></p></blockquote><br /><br />BTW, I hope everyone realize I was not being serious at all with this statement. Failing to get any reactions at all, I am afraid that some may take this statement seriously.<br /><br />This one goes in line with it's better having the shuttle comes back to earth at night, because it is cooler for the re-entry. <div class="Discussion_UserSignature"> </div>

 

[PistolPete]

That depends on the reentry speed. The F-15 and MiG-25 have gone higher than the NF-104 (the Ye-266, a MiG-25 prototype, still holds the world absolute altitude record for a jet at 123,523 ft.) and neither of these two jets required any additional thermal protection. Also note how little ablative protection was required for SpaceShip-1.<br /><br />The thermal load on the X-15 wasn't that great on high altitude flights either. Most of the extreme heating that the X-15 endured was caused by high speed flights which used a much flatter trajectory at lower altitudes.<br /><br />If it's maximum altitude that you are trying to achieve, then thermal loads are not much of a concern because most of your inertia is spent trying to reach max altitude. However, if you are trying to impart some delta v on a second stage, like the Pioneer Rocketplane's Pathfinder, then thermal protection becomes more of a concern, but that is not an insurmountable problem.<br /> <div class="Discussion_UserSignature"> <p> </p><p><em>So, again we are defeated. This victory belongs to the farmers, not us.</em></p><p><strong>-Kambei Shimada from the movie Seven Samurai</strong></p> </div>

 

[propforce]

PistolPete,<br /><br />Man I am impressed with you. A person in the U.S. Army calvary who can survive in the desert, drink his own sweat, shoot bad guys, and has a firm grasp of physics and space history.<br /><br />I wanna work for you when you become a colonel someday <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> </div>

 

[scipt]

Petes not an ordinary 'squadie' he's a student too. I don't know what his subject is, but he's damned smart. <div class="Discussion_UserSignature"> </div>

 

[PistolPete]

You'll never guess what my major is. Sometimes I can't believe that I'm studying it myself. <div class="Discussion_UserSignature"> <p> </p><p><em>So, again we are defeated. This victory belongs to the farmers, not us.</em></p><p><strong>-Kambei Shimada from the movie Seven Samurai</strong></p> </div>

 

[PistolPete]

Remember that show on Nickelodeon called <i>Salute Your Shorts</i>? I'm Sponge. I absorb knowledge like a sponge, and if you squeeze me hard eough, it comes spilling out. <div class="Discussion_UserSignature"> <p> </p><p><em>So, again we are defeated. This victory belongs to the farmers, not us.</em></p><p><strong>-Kambei Shimada from the movie Seven Samurai</strong></p> </div>

 

[j05h]

> You'll never guess what my major is. Sometimes I can't believe that I'm studying it myself.<br /><br />Basket-weaving with a minor in psychology? <img src="/images/icons/wink.gif" /><br /><br />Seriously, I'd guess you are doing some form of applied engineering: EE, aero, maybe civil or architecture. How far off is the guess?<br /><br />Josh <div class="Discussion_UserSignature"> <div align="center"><em>We need a first generation of pioneers.</em><br /></div> </div>

 

[PistolPete]

Waaaaaay off. It's not even funny. <img src="/images/icons/laugh.gif" /> <div class="Discussion_UserSignature"> <p> </p><p><em>So, again we are defeated. This victory belongs to the farmers, not us.</em></p><p><strong>-Kambei Shimada from the movie Seven Samurai</strong></p> </div>