Depending upon the amplitude of the Ares-1 vibration (a solid rocket motor can act like a pipe in a pipe organ) and whether current satellite designs can withstand such vibration, they may not have to “re-tune” the rocket motors by using fewer segments than Aries 1 used.

So does the fact that SLS’s projected flight rate is so low, even if it’s never cancelled, that Orbital won’t be selling many SRB segments for that purpose. Thus, Orbital has a considerable incentive to find ways to use more segments produced at marginal cost.

Using the VAB and an MLP means also using the NASA crawler-transporters that were recently upgraded to handle SLS and, of course, using the only remaining launch facility where these other items can be employed, namely Kennedy’s LC-39B. NASA has said it will share SLS’s home pad with commercial users. Looks as though Orbital aims to be the first – and perhaps only – such time share.

The Ares-1 famously suffered from vibration issues. This new rocket won’t carry people, but national security satellites probably don’t appreciate a cement-mixer-esque ride to orbit any more than human bodies do. Perhaps Orbital will dodge the worst of the vibration issue by using two booster stages, each based on two SRB segments, instead of a single booster stage with four or more segments.

The interest in the VAB and mobile launch platform (MLP) stems from the fact any EELV-class vehicle based on SRB segments as lower stage booster(s) will be a lot heavier than any comparable liquid-fueled vehicle. The beast must be stacked from mostly heavy parts and national defense payloads require vertical integration with their boosters anyway.

I’m dubious about the long-term viability of this whole scheme, but if it works out, Orbital could conceivably take an additional VAB high bay and MLP off NASA’s hands a few years hence if the launch cadence becomes sufficient to require this. It’s always good to see expensive sunk-cost government facilities repurposed to support commercial endeavors.