Ares I and GEM

[wtrix]

Hi!

I found myself wondering about one important design decision on Ares I. As it was found out that current SS SRB with 4 segments is not enough to propel Orion in to orbit why they opted to add fifth segemnt and thus, redeseign the SRB instead of just adding multiple GEM-60 motors around the lower part of the SRB together with reduced burn area in start burn of the SRB. It should have been possible to make a launch profile similar to 5 segment SRB this way. Does anyone have some knowledge why? did they consider this option at all?

 

[Swampcat]

If you can figure out a way to attach solid rocket boosters to the Ares I first stage without the aft skirt getting in the way you might be on to something.

 

[wtrix]

If you can figure out a way to attach solid rocket boosters to the Ares I first stage without the aft skirt getting in the way you might be on to something.

Why doesn't the attatchment frame suite? You can build a spacer frame in betbeen the SRB and GEM's. Plus, to save mass, you can attatch the GEM-s with minor inwards inclination.

Another option is to replace the aft skirt with fame for actuators and start site bolt attatchments. Fact is that you don't need the separation motors anymore anyhow. Thus you can have at least four open sides for direct attatchment of GEM-60. I haven't run any calculations, but gut feeling says that 4 GEM-60 rockets plus more propellant in SRB (resulting from smaller burn area at the start) is enough to replace the fifth segment.

One more possibility - this configuration may lead to less vibrations and shaking, thus, eliminating the need for dampers. that saves additional mass.

 

[docm]

On the other hand the thrust oscillations of the GEM's, and/or their harmonics, could interact with those of the SRB and shake the whole shebang into small pieces.

 

[wtrix]

On the other hand the thrust oscillations of the GEM's, and/or their harmonics, could interact with those of the SRB and shake the whole shebang into small pieces.

They could, but due to size differences, I don't believe this scenario of being probable. Nonetheless. Both systems are more or less tested and their acoustic profiles are known. Thus the resulting resonance patterns can be calculated.

 

[wtrix]

Does enyone have any ideas why? Safety reasons? NASA seems to avoid strap-on boosters nowadays.

 

[Boris_Badenov]

Does enyone have any ideas why? Safety reasons? NASA seems to avoid strap-on boosters nowadays.

Take this question over to NASA Spaceflight & ask the NASA Engineers directly.

 

[matthewota]

I would be willing to bet that strap-ons were considered. But from an economics standpoint, it is likely less expensive to add a fifth segment. The Ares are supposed to be shuttle derived to save money.

 

[radarredux]

The Ares are supposed to be shuttle derived to save money.

I've been wondering about the justification of this argument lately. Based on the Augustine Panel's model, the Ares I would not be ready until ISS was splashed (it turns out this is the case whether ISS is splashed in 2016 or 2020), and then it would be 7-8 years after that before Ares V would be ready. And even if Ares I is cancelled in favor of commercial launch services, IIRC Ares V would not be ready for missions until ~2022 (for a 2016 splash of ISS) and ~2028 (for a 2020 splash of ISS).

So the most likely scenario (keeping ISS until 2020) means that NASA won't be flying any missions with Shuttle-derived rockets for ~18 years after the Shuttle is retired. With that in mind, does basing your system of the Shuttle still really save money?

 

[docm]

The argument could be made it never saved money even on the original schedule.

 

[zacksdad]

Does enyone have any ideas why? Safety reasons? NASA seems to avoid strap-on boosters nowadays.

ARES 1 is a strap-on booster....

:lol: