Yes, I very much want to cluster some of these!
This vehicle should be able to handily get past 100km, even though we are going to be conservative on the first flight attempt and just be happy to exceed 100,000'. We have lots of fairly straightforward axis for improving the performance -- fair over the exposed bits to reduce drag, increase the nozzle expansion ratio, move to one of our newer injector designs, and, of course, take weight out of it.
Once we show that the vehicle can clearly fly to space, clustering will improve the payload fraction -- two tubes = a single computer box and no roll vane (differential gimbal like titan), four tubes = fixed engines with better plumbing flow and less actuators, etc.
The first order of business is launching and recovering it successfully. Doing sub scale drop tests from an airplane has been helpful, and may have already saved the real vehicle with what we learned.
For reasons that still aren't exactly clear to me, this vehicle took longer to build than any of our previous ones. With all the full time salaries, that also makes it the most expensive vehicle we have made. I have said that watching one of our serial-produced mods crash from an altitude flight is "like watching a BMW fall out of the sky". Losing this vehicle will be more like planting a Ferrari. A turbo Ferrari. Realistically, it is almost inevitable. If we get a successful first flight, everything will work out fine, but I imagine the mood in the shop will be pretty grim while building up a new version of this vehicle if all we got out of the previous one was a couple hover tests and a crash.
Despite being extremely upset with how long it took us to get to flight-ready, I find myself now wishing we had another week to run additional tests, but we have already postponed launch once at Spaceport America, and we really should take our shot now.
Yesterday I did wind up running a final set of tests on the rocket to put my mind at ease about the sequencing of the recovery system by the flight computer. The test showed that it was doing exactly what we wanted, but in the process of modifying things to fake the computer into thinking it was falling from 35km while it was in the shop, I wound up breaking into the debugger while one of the igniter solenoids was powered on, and burned it up, resulting in the need to make a last minute part swap on an otherwise ready-to-ship rocket.
I hate using NOS solenoids because they aren"t continuous duty, but the initial configuration of the vehicle had the igniter in an orientation where that was the only solenoid that would fit. We wound up changing the igniter position later for unrelated reasons, so we could have used a GEM or predyne solenoid if we had thought about it, but we didn't.
The rocket is on the road to Spaceport America today, everything looks good. Because we came in overweight and are running a fairly low tank pressure, we will be eating a lot of gravity losses on the vehicle, but that also means we won"t have a really crushing max-Q. Sims say we should comfortably clear 100,000", but I wouldn't be stunned if it underperformed.
The mention of weight prompts one of my usual bits of advice for newcomers:
Essentially every single time you make a decision with "flight weight" as a deciding factor, you are making a mistake. Pushing for flying something instead of just doing test stand work is important, but you are many, many generations away from building some mass-ratio 8 vehicle where you are shaving every gram of weight. There is over an order of magnitude difference between what commercial orbital vehicles need to care about with respect to weight and what a new comer to experimental liquid rocketry should be caring about. A liquid fueled rocket can fly just fine with a mass ratio of 1.25.
Go for the solution that looks easiest, with almost no regard for performance. It will turn out not to be easy, but if you lowballed your expectations enough, you might actually succeed in making it fly, instead of winding up with a failed and abandoned project.