sevenperforce

Crush cores will be used on all, most likely -- they are reusable as long as they aren't used.

So do they still drop straight down? Those looks like crush cores.

I wonder if it would be possible to do a lithostaged Munar touch-and-go using a twin boar and the internal RCS on the MEM capsule.

The jet intakes all have suction at zero forward airspeed. On the other hand it becomes a "whose computer can handle the highest part count" challenge, which is not as interesting. To make it more interesting you could do a "no parallel staging and no engine more than once" rule which would be very interesting.

Wholly practical. They are already used, in fact. The X-43 has one half of a linear shock cone forming its entire forebody.

Or leaving the interior empty and manifesting a 5 tonne module externally.

I don't think it will be though. I think it will. Single payload adapter/docking ring/propulsion unit.

We don't know whether that 5-tonne payload is limited by injection dV (FHUS) or insertion dV (vehicle). Let's start with the assumption that the 5-tonne payload is limited by the insertion dV. It takes 430 m/s to go from TLI to the gateway...let's pump that up to 500 m/s for margin, rendezvous, docking, and so forth. Dracos develop 300 s of specific impulse. The Dragon XL would need to burn 15.6% of its mass as propellant to generate 500 m/s, and the Dragon 2's propulsion package has 1388 kg of propellant, so that's a total vehicle wet mass of 8.9 tonnes. With 5 tonnes being payload and 1.38 tonnes being propellant, that leaves a vehicle dry mass of 2.51 tonnes. Dragon 2 has a dry mass of 9.53 tonnes. Does that mean ECLSS+heat shield+aeroshell+ballistic sled+parachutes total a whopping 7 tonnes? Or are we looking at a vehicle with higher propellant capacity?

Looks like the depiction has the same docking port (with four Draco RCS thrusters) as Dragon 2. There's probably a 75% chance this has the same exact propellant tanks as Dragon 2, just with the aeroshell and heat shield and chutes removed. Might be useful for estimates.....

We spend too much time close to Kerbin -- it's time to think beyond! I was building a Sepratron-powered orbiter for this excellent challenge: When I used my crewed rocket with just a probe core instead, I discovered that I was very nearly interstellar. Adding two extra stages and a few more tweaks got me out of Kerbol's SOI on a Sepratron-only rocket massing just over 16.2 tonnes. It made me think...what are the limits of going interstellar? Who can go interstellar with the lowest liftoff mass? Who can get interstellar the fastest? Who can go interstellar with the fewest parts? Who can get onto an interstellar trajectory as low as possible within Kerbin's atmosphere? Is it possible to take an SSTO to Kerbin's atmosphere without staging? What is the lowest mass-to-interstellar without using nukes or ions? Rather than doing a leaderboard with this challenge, I was thinking of doing a challenge-within-a-challenge. Each entrant should post an interstellar vehicle optimized for whatever they are good at and challenge other entrants to beat them. I'll kick it off -- go interstellar in under 16 tonnes!

Just put Jeb into orbit with a 6.997 tonne rocket but getting him back to Kerbin is tricky. Six stages, like @qzgy, but distributed a little differently. All motors are inside one of the two fairings.

With MHD you are still limited by intake area. It's always going to be better to just use an initial propellant dump to get up to speed. Either that or a rolling start.

The upper limit on pusher-plate specific impulse is somewhere around 12,000 s. The upper limit on the specific impulse of an antimatter rocket is somewhere around 15,000,000 s.

Yeah, 2-3 million dead in the U.S. alone. 7 billion infections worldwide.

In order to "suck in" air, you need to lower pressure at your inlet. You can do that with a big-ass turbofan/turbocompressor, or you can use the Coanda effect or laminar flow. The important thing is that you only need that high mass flow for a very brief period of time. Once you have velocity, the ram effect will do compression for you. So if you have an engine design that can vastly boost thrust for a short period of time without increased dry mass (maybe with lower specific impulse), you just boost hard during the first 30-60 seconds of flight and then you're good. You need the entire forebody of the spaceship to act as a shock cone intake for forebody compression.