Space Forum / Shuttle / June 2004

That would be OK for an inspection, although it's more difficult than one
might think: for instance, you don't want your remote-controlled device to
bump into the orbiter, or to loose radio contact with the crew. But what
about a possible repair? There, you need the boom anyway.

    Jan

thats a obvious answer and would be useful for ISS exterior inspections too.

NASA backing off  the recommended safety improvements has me concerned
HAVE A GREAT DAY!

The short answer is that there is no way NASA could get such an autonomous
camera (AERCam) ready to fly before the boom (OBSS) is ready. It would
delay return-to-flight at least another sixteen months.

NASA originally selected OBSS for several reasons. Since it's fixed to the
orbiter's robotic arm (RMS), the position of the tip is always well-known
with respect to the structure it's examining, and it's also possible to
pause the inspection at any time merely by putting the brakes on the arm.
As Jan points out, it also offers a growth path toward standalone repair
capability: with proper tip stabilization, you could put an EVA worksite on
the boom to repair damage without relying on ISS.

The camera you are referring to, which NASA has already been working on
(AERCam/Sprint), had serious limitations with regard to inspection. It
required an EVA for deployment/retrieval, which restricted it from being
used early in a mission. It lacked any kind of relative navigation sensors,
and its guidance/control system was almost completely manual. An inspection
with AERCam/Sprint would have been a tedious and risky affair, requiring an
EVA, and requiring the pilot to meticulously hand-fly the AERCam around the
structure for hours.  Loss of comm during the flyaround (or merely pilot
inattention at the wrong time) could result in the AERCam drifting away and
being lost, or worse (again, as Jan points out) a collision between AERCam
and the orbiter.

Nevertheless, NASA is giving AERCam another look. There are several
circumstances that have changed to cause this.

First, it has been discovered that on several ISS assembly flights,
starting with 120/10A, there is insufficient clearance to berth OBSS in the
payload bay, so OBSS cannot be carried on those flights. This is the big
driver: *some* kind of OBSS alternative is required by 10A, period.

Second, the cancellation of HST SM-4 has reduced the urgency of developing
standalone repair capability (at least in the minds of shuttle program
management - the CAIB's opinion may differ). So the growth path to
standalone repair offered by a boom no longer looks like such a big
advantage.

Third, the shuttle program plans to install accelerometers and strain
gauges behind the leading edge of the wing to detect impacts during flight,
and they hope to have this capability completely validated by the time OBSS
can no longer fly. This would eliminate the need for a full inspection of
the leading edge; inspection could be concentrated on areas where damage is
known or suspected. The program would rely on the Rbar Pitch Maneuver (RPM)
to allow the ISS crew to photograph damage on areas of the underside other
than the leading edge.

Fourth, the AERCam team has proposed a successor to AERCam/Sprint (Mini-
AERCam) that addresses most of Sprint's limitations. It has a payload bay
hangar for deployment/retrieval (no EVA required), relative GPS navigation
(untested in space, unfortunately...), and a guidance/control system with
capabilities for relative attitude/position hold, as well as a "backtrack"
mode in case it loses comm with the orbiter. Driven by the need for an OBSS
alternative by 120/10A, the AERCam team proposes to test their concept on
119/15A, and "go operational" on the next flight. This is a highly
ambitious schedule. It is completely out of the question that they could be
ready for 114/LF-1 unless that flight were slipped from its current launch
date (3/6/05) to where 119/15A is now (7/13/06), a slip of sixteen months.