Entry Tutorial

Entry Transition Phase

Transitioning from entry flight to more "normal" supersonic gliding.

Home | Deorbit and Coast | Initial | Peak Heating | Constant Drag | Entry Transition | Approach and Landing


Drag here is a bit high, and it eventually caught up with me later on.  I'm gonna have to do a roll reversal soon,  As roll reversals happen at slower speeds they become less tricky as more control authority is attained from increasing dynamic pressure (currently 292 psf), roll angles become smaller, sideslip in sharp banks become more noticable, and it becomes impossible to exit the atmosphere without applying power, even on purpose.  In short, your ship is turning more and more into an gliding aircraft rather than a controlled meteor.
In the Delta Glider, this transistion is gradual, but obvious.  The ship's sink rates will go up to maintain the constant drag gradually as she need the thicker air at lower speeds.  She wants to actually turn rather than "just crossrange."  The reason is that as speed goes down, it becomes easier and easier to affect direction.  Any driver's safety course will allude to the turning formula v^2/r, sometimes without realizing it.  A turn of the same radius require's twice as much directional accelleration with each 40% increase in speed...a turn at twice the speed is four times as forceful.  In the Delta Glider, this is happening in reverse.  With each 40% drop in speed, and from 5 miles a second, there's obviously a lot of speed to drop, she wants to turn nearly twice as tight.  I say nearly because Delta Glider's L/D ratio is dropping as she goes down to the transonic region.
In the transition phase, the angle-of-attack continues to ramp down, reaching about 14 degrees as the Orbiter reaches the Terminal Area Energy Management (TAEM) interface, at approximately 83,000 feet [25,300km] altitude, 2,500 fps (1,700 mph) [760m/s; about Mach 2.5], and 69 miles [111km] from the runway.  Control is then transfer to TAEM guidance.
(Capitalization added to what TAEM stands for.)
SpaceShipOne makes its transition extremely obvious by using a high-drag, low-lift dynamically stable "shuttlecock mode" by tipping its collossal elevons and fins up.  The transition from entry is marked by SpaceShipOne folding these huge surfaces back to their normal flight positions.
On ballistic spacecraft, this transition is marked by parachute deployment.  Generally no matter what type of ship you fly, the transition happens somewhere between Mach 2 and Mach 7.
An entry damage induced breakup in Shuttle becomes possible to survive.  At some point, the cabin would survive post breakup heating and aerodynamic forces so that the crew could blow the hatch and use their parachutes.  If Challenger were equipped with the modern escape equipment (the David Clark Co. S1035 Advanced Crew Escape "Pumpkin" Suit (ACES) and the pyro ejectable hatch, it is quite likely that some of her crew would have been able to escape the tumbling cabin and survive the disaster.  On STS-107, this equipment plainly did not make any difference, and would not have even if it were all being used properly as the cabin broke up under 5-6g loading and Mach 12 at about 100,000 feet.  (According to the Crew Survival Working Group, 3 astronauts didn't have their gloves on, and one mid deck astronaut, After Columbia suspects David Brown, did not have his helmet on.)


Here over the Florida panhandle, I am far from home free just prior to aquiring KSC's navigational transponder (VOR/ILS in pilotspeak).  My glide ratio shown as "GLIDE", a value computed by my trusty EL-546 pocket flight computer (distance divided by altitude) is far too high.  A powered landing will (once again) be required.  Doing this over and over and over again in Martin Schweiger's free simulator gives one an appreciation as to why flight controllers calculate to within fifty feet exactly where the wheels will touch the runway on this 2 billion dollar plus unpowered gliding brickyard returning from its 600 million dollar plus mission (with cryptic terms like X-corrected Normalized with CLOSE and DDS.)


The reason why my version of Delta Glider TAEM is so tricky is because I'm trying to line up with the runway and manage energy at the same time.  My most successful approaches (not this entry) involve lining up the right distance out at about 50km and 20km altitude as I go subsonic, and then generously using the airbrakes (Ctrl-B) on the way in.  Valid glideslope angles for approach from 20km altitude are from 15 degrees up to about 40, leaving about a 45km window to go subsonic between 30 and 75km from the runway threshhold.  GLIDE above right now ought to be about 4-5, but I didn't realize it was that bad for a couple more minutes as I bleed speed to maintain altitude at maximum lift elevon control...creating the illusion that I could get closer to the runway than I really could.  Under circumstances not quite as bad, this could lead one to believe he can make the runway when really he can't.  As you can tell, I need to refine my technique.

It is unfortunate that the ILS glideslope can't be adjusted for returning spacecraft...

You can see that my GLIDE value has come down considerably as a result of trading speed for altitude, but I now estimate that I am about 30 km short of the runway under these circumstances for an unpowered glide landing.  This shot was taken during the transonic transition period, where the Delta Glider's lift over drag is lowest at about 2.2.

All cyan colored text throughout the tutorial (excuding headers and footers) is quoted from
Dennis R. Jenkins' Space Shuttle: The History of the National Space Transportation System, the First 100 Missions, Motorbooks International and others, 1989-2002, pp. 260-261.

2004 After Columbia