credit: NASA / caption: Shuttle SRB aft skirt's thrust vector control hydrazine powered hydraulic system
On 5 August NASA released a pre-solicitation synopsis for a Request for Proposal (RFP) for its Ares [I crew launch vehicle solid rocket booster (SRB) first-stage] electric thrust vector control (TVC) prototype risk reduction system requirement - more easily written than read
Its another example of how the CLV's first-stage will bear little resemblance to the original Shuttle SRB. From memory, I think, a change to an electric TVC would literally mean the only original bit of the Shuttle SRB design to remain will be the steel segment casings
For years TVC electromechanical actuators (EMA) have been investigated because NASA believes they are lighter, cleaner, possibly even safer in their operation, and are easier to maintain than the hydrazine powered hydraulics used by Shuttle today
NASA was conducting research into electric TVCs almost 20-years ago and Marshall Spaceflight Center produced this report in 1993
credit: NASA MSFC / caption: the 1993 report produced this schematic of the actuator
The key word to focus on today is lighter. If you are adding mass to the vehicle with an oscillation mitigation system then you might want to think about ditching that dirty great hydraulic system, yes?
But another thought comes to me. NASA is talking about an active mass damper system that will need power. I wonder if there are benefits in having an electric TVC not only for mass savings but in terms of sharing the power source that will enable the two systems?
With NASA concluding 20-years ago that Shuttle readiness could have been shortened by 10-days by avoiding the TVC hydraulic system prep with an all-electric operation you wonder why they didn't opt for EMAs for Ares I in the first place?
And then another mystery, as the agency suspends the EMA/TVC solicitation. "NASA has determined to put the subject acquisition on hold pending further agency reviews. It is anticipated that a decision will be made no later than October 1, 2008," the agency announced on 28 August. Isn't that after the Ares I stack preliminary design review ends...?
on September 5, 2008 7:40 AM | Reply
Exactly, it's in case they're overmass at PDR and need to drop some mass real quick...
on September 5, 2008 6:05 PM | Reply
EMA's tend to be heavier then hydraulics, which is why
cars, airplanes, and launchers have used Hydraulics
instead of electricals.
EMA's help you on turn around, fewer leaks, a lot more reliable
and computer guys like them.
I suspect the EMC's are cancelled because they did a detailed weight
study and decided they were too big or too heavy.
on December 11, 2008 10:31 AM | Reply
EMA's are heavier than hydraulic actuators but the electromechanical TVC are definitely lighter than the electro hydraulic TVC!
Problem of EMC is usually not that critical if elec TVC is powered by batteries that supply only the TVC. However if the batteries supplies other devices it's indeed critical as those high power TVC reject lots of disturbances on power lines.
The real problem of that kind of electric TVC are:
- no simple solution for supporting high transient loads on the rolls(for hydraulic just a bypass valve between piston chamber)
- electrical insulation (corona effect)
- price!
on May 27, 2009 4:22 AM | Reply
weight is definitely an issue specially on launchers but then again its one heck of a piece of technology