20
$\begingroup$

This answer to Who are the actual lead designers of manned spacecraft? says (in its entirety):

Max Faget was involved in the design of every US manned spacecraft flown to date. Mercury, Gemini, Apollo, and Shuttle. It looks like Elon Musk will end Max's monopoly.

and that Wikipedia article contains the image below.

Question: Suppose the Space Shuttle's form factor was pretty much like this, which is reminiscent (in my opinion) of a low speed propellor-driven aircraft for carrying mail or freight. While suboptimal, how well would it have worked if it was tried? What would have been the major problems and challenges to making it work if for some reason it was tried?

"Bonus points" for addressing the specific date of the design's release.


Max Faget's April 1, 1969 design for the Space Shuttle

source

Space shuttle model, created by Dr. Max Faget, April 1, 1969 - Kennedy Space Center - Cape Canaveral, Florida

The caption in the Wikipedia article says something similar:

Space shuttle model, created by Faget, April 1, 1969

$\endgroup$
10
  • 1
    $\begingroup$ "While suboptimal"? $\endgroup$ Jun 9 at 4:18
  • 2
    $\begingroup$ Three things I find odd about the model. The wings look like they are backwards. The leading edge of the wings is perpendicular to the fuselage & they're square cut at the ends. The other thing is, the wings appear to be to the rear side of the center line of the fuselage. It would be interesting to know what the thoughts were about the center of gravity of the craft. $\endgroup$
    – Fred
    Jun 9 at 5:48
  • 2
    $\begingroup$ I'm still half-convinced this whole thing is some sort of prank. $\endgroup$
    – SF.
    Jun 9 at 9:27
  • 17
    $\begingroup$ Clearly it would have burned up on entry because it's made of paper and wood. $\endgroup$ Jun 9 at 16:55
  • 1
    $\begingroup$ I don't know this source material well enough to distill it into a good Stack Exchange answer, but NASA's historical book The Space Shuttle Decision (PDF) details how the evolving requirements of the shuttle influenced its basic configuration, including wing shape. Faget's designs feature heavily starting around chapter 5, for example. $\endgroup$
    – Maxpm
    Jun 10 at 23:08
17
$\begingroup$

Mission Requirements for a spaceplane that are affected by its aerodynamic shape

  • Cross-range capability
    • Gliding range perpendicular to orbital plane on reentry. Otherwise, you have to wait in orbit for the earth to rotate your landing site into alignment with the orbital plane.
  • Flying Qualities
    • How easy the spaceplane is to fly.
  • Landing Speed
    • Safe speed for landing, which then determines runway length.
  • Reentry Maximum Structural Loads
    • How much reinforcement (extra mass) is necessary for the airframe to withstand reentry aerodynamic forces.
  • Reentry Thermal Loads
    • Superheated plasma formed at the bow shocks at the windward surface of the spaceplane radiates heat into the airframe. If this gets too intense or persists for too long, components can overheat or otherwise be damaged.

To simplify this answer, I won't go into launch aerodynamics.

Stages of a typical spaceplane reentry and landing to be aware of

  1. When starting to get into the thin atmosphere many minutes after the reentry burn, the spaceplane is put into a high-AoA position for high drag to slow down quickly enough to not exceed the structural or thermal loads limits later in the reentry. The roll of the spaceplane can be adjusted to begin turning the spaceplane away from its orbital plane (cross-range).
  2. After passing the hotter parts of the reentry, the spaceplane lessens its AoA and basically becomes a glider, albeit with much worse performance than a purpose-built glider. It is still high-altitude at this point, so it has significant cross-range capability to exploit, while either supersonic or subsonic.
  3. The approach and landing of the spaceplane is like any glider, just at a higher speed.

Comparison to actual Space Shuttle

The fuselage of this model is not significantly different to the actual Space Shuttle, so I will not comment on its performance.

The wings, however, are high aspect ratio cambered airfoils with a conventional trapezoidal taper. The high aspect ratio and trapezoidal taper reduces induced drag. These wings are efficient and performant at subsonic speeds, which is a benefit over a delta wing for subsonic flying qualities, landing speed, and cross-range capability while subsonic.

These wings are more difficult to reinforce per-area against high-AoA hypersonic reentry aerodynamic loads than a delta wing because of their high aspect ratio. They also increase heat insulation requirements for the spaceplane as a whole as they do not shield the fuselage above them as much as a delta wing.

These wings are less efficient than a delta wing in low-AoA supersonic glide due to their tips most likely jutting out of the cone of already-disturbed supersonic flow from the nose. This results in more wave drag, which decreases cross-range capability and increases aerodynamic loads. The wings not being swept back results in more drag due to the Area Rule (sharp changes in cross-sectional area = more drag). During transonic (Mach~1) flight, the wings produce less lift due to the Critical Mach Number being lower on non-swept wings.

The horizontal tail has the same issues as the wings in supersonic flight, but the dual vertical tail with large forward-canted rudders is great for supersonic/hypersonic flying qualities at high AoA.

In Summary

These are subsonic-optimized wings which would likely make landing easier than with a delta wing. They sacrifice critical reentry heating and supersonic glide performance, which reduces cross-range capability and supersonic flying qualities, while increasing reentry structural loads and reentry thermal loads. While you could probably make a shape like this work, the resulting spaceplane would not have much payload mass capacity due to extra dry-mass necessary to mitigate the above issues. It is possible that, for this model design, there was another requirement on the landing conditions that mandated a subsonic wing.


References:

$\endgroup$
9
  • 1
    $\begingroup$ My understanding is that the straight wing would decrease, not increase, landing speed, and reduce the total heat load of reentry by shortening the reentry time frame. The wing itself would also be lighter than a delta. Why do you think it would reduce the cargo capacity of the shuttle? $\endgroup$ Jun 9 at 23:05
  • $\begingroup$ @RussellBorogove Thanks for catching the landing speed comment, that was an error (in the summary). I think this wing has less area than one that looks like the Shuttle's delta wing, which would mean less drag from wind-frame area at high AoA, lengthening the duration of reentry heating. This wing could be lighter than a delta, but is less efficient in mass per area. The leeward side of the shuttle fuselage (above the wings) has lighter insulation due to the protection from the long wing strake and delta wing. Extra mass needed to compensate for these issues would reduce payload mass. $\endgroup$ Jun 9 at 23:14
  • $\begingroup$ Less drag but far less lift in the nose-up reentry attitude, for a much faster descent. See the plot in my answer. $\endgroup$ Jun 9 at 23:16
  • $\begingroup$ @RussellBorogove the Shuttle made use of its lift for cross-range capability or negated it by using S-turns. The straight wing would have a faster descent if kept nose-up with no roll. $\endgroup$ Jun 9 at 23:19
  • 1
    $\begingroup$ And the extreme cross-range capability that USAF insisted on wasn't used. $\endgroup$ Jun 9 at 23:21
16
$\begingroup$

The straight wing concept was perfectly workable. According to The Space Shuttle Decision, Max Faget preferred the straight wing approach primarily because it would optimize performance in the final subsonic approach-and-landing phase.

The straight wing would also provide very little lift in the high-speed, nose-high reentry phase, meaning it would fall very quickly, and the heating period would be much shorter, making for less total heat load. In this plot the reentry heating of a straight-wing orbiter with lift-to-drag ratio of 0.5 is shown versus a delta-wing orbiter with lift-to-drag ratio of 1.7:

enter image description here

On the flip side, the long reentry of the shuttle's delta wing made for a very gentle ride, with reentry g-load peaking at about 1.2g. A straight-wing shuttle would have incurred much higher g-forces, but not prohibitively high. The turbulent airflow around the wing during reentry would also increase peak temperatures on the sides of the orbiter's fuselage, partially offsetting the savings in thermal protection gained by the shorter reentry.

Another small, subtle advantage of the straight-wing orbiter design is that changes in weight and balance during development can be more easily addressed by slight changes in the position and/or sweep of the wing with little impact on the overall design, as opposed to the more extensive wing-body integration of a delta-wing design.

Air Force scientists were opposed to the straight wing. During the transition from nose-up reentry to horizontal flight, the wing would be stalled, and the shuttle would lose about 15,000 feet of altitude before regaining control. The delta wing would keep the orbiter's flying characteristics changing more gradually as it transitioned from reentry to supersonic to subsonic flight. The delta wing was also necessary to achieve the Air Force's high crossrange requirement (allowing the orbiter to maneuver 1000 miles or more off its reentry flight path), but the extent of that crossrange capability was never used by the shuttle. NASA had originally wanted 250 to 400 miles of crossrange; the higher the crossrange capability, the more opportunities for reentry and safe landing in emergency situations. Faget's original straight-wing concepts could achieve the low end of that crossrange specification, and a slightly larger wing could extend that.

Dozens of general layout concepts for the shuttle were proposed during this general time period, until the final selection of a configuration in 1972. Several of them are illustrated in The Space Shuttle Decision, and many others in Dennis Jenkins' book; here are a few of the early ones:

Three-view drawings of six proposed straight-wing orbiter configurations, a straight-wing flyback booster, and a booster-orbiter combination. The designs are dated from April to September 1970.

Up to mid-1971, straight-wing designs dominated the proposals despite the Air Force's opposition. Most of the proposals from mid-1971 on were deltas, though Faget slipped a few more straight-wing designs into the mix after that.

I don't see any concepts in Jenkins with a completely unswept leading edge and slightly forward-swept trailing edge, as on this model, and most of them were single-tail instead of twin-tailed.

A straight-wing orbiter would not have satisfied the Air Force's crossrange requirement, but apart from that, there's no fundamental reason it couldn't have been a successful space shuttle.

$\endgroup$
9
$\begingroup$

The design looks like it was descended from silbervogel, a German world war II projectsilver bird drawing source The twin tails would have been to maintain control at high angle of attack but it appears the advantages of blunt body shapes for re-entry heating control were not understood giving it straight wings with sharp edges.

The possibility of a delta design was only being developed at around the same time, and the Silvervogel design team may not have had access to the aerodynamic work behind them, or seen a need - the design proportions were probably based engineering work for very high altitude conventional aircraft

What is odd is making a model in 1969 when re-entry and delta wings were understood with Von Braun's proposed space planes in the early 50s and Dynasoar in 1965Dynasoar source

Using familiar shapes.

Unsourced speculation is that this is either a much earlier Silvervogel model used as part of a larger collection of space plane designs by Dr Faget in 1969, or was built in 1969 as a 'how well would it have worked' project for personal interest. Note that the model is wood and doped paper so completely useless for serious supersonic or hypersonic windtunnel work, and appears to have a nose weight for free flight gliding.

$\endgroup$
9
$\begingroup$

The model itself did get some flight testing.

Faget toss #1

Faget toss #2

$\endgroup$
2
  • 4
    $\begingroup$ Nice find, but can you provide a source and some context for the photos? Welcome to the site! $\endgroup$ Jun 10 at 16:29
  • $\begingroup$ From a reverse image search: rnasa.org/photos_2004_and_earlier.html#1987. There doesn't appear to be much context (from a awards ceremony/conference it seems like?). (note that Moon Watcher's image are clickable and go to that site as well) $\endgroup$
    – Modelmat
    Jun 11 at 7:26

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.