RCgothic

Alert notice posted for tomorrow:

Yes, that much better. I thought up that point after realising comet 2014 UN271 doesn't come inside the orbit of Saturn. Also your original definition would define anything that even *slightly* crosses Mercury's orbit as a comet. Most things that close to the sun would be perpetually baked and barely outgas at all. The key feature of comets is the outgassing I feel.

I take biggest issue with this definition. Halley's comet (Perihelion 0.59AU) would therefore not be a comet because it doesn't cross the orbit of Mercury (Aphelion 0.47AU)?

Now do multiple moons with eccentric inclined orbits. ;-)

No, it means there are two orbital launch sites planned at Boca! Although I do actually think there's a good chance of a Hammerhead crane stacking on top of level 8.

Tower gets its final level.

So there's a giant comet we discovered a few years back is now on the way to making its closest approach to the sun somewhere just beyond the orbit of Saturn in Jan 2031. This guy calculated some DV figures, for flyby or rendezvous: So I'm interested. Firstly are these figures right? 2033 is somewhat after perihelion. Could we get a mission to the comet before perihelion in 2031? What would that take? And do we even want to get there before? Does the period of maximum activity lag perhelion much the same way the hottest days of the year lag summer solstice? Secondly, a minimum C3 of 113 is a big ask, and minimum 12.5km for a rendezvous would be the largest ever deep space DV manoeuvre. How would you guys assemble a mission to the comet? Flyby or rendezvous? Is rendezvous even possible with current launch vehicles? I have some ideas of my own that I'm currently calculating, but thought I'd start a discussion before steering in any particular direction. :-)

Cryo test

As far as I'm concerned, whether it's 100km or 80km doesn't make much difference except in time of weightlessness. Any suborbital flight is still a 1XP activity compared to an orbital flight of 2XP.

The planetary protection stuff isn't ultimately because we don't want to spread life to other planets. If we're going to live in other worlds they're going to get contaminated, and any effort to prevent that is ultimately futile. The reason we currently go to such lengths is so that future probes don't go "we've discovered native life!" when in actual fact they're discovering the results of previous probes. But starship could definitely deliver something hefty to Enceladus. It's 7300m/s to Saturn and 3600m/s to Enceladus from LEO. That's ~11km/s total. DeepSpace!Starship probably weighs about 60t dry and pushes 100t payload and 380s ISP. With 1200t of propellant it can get to Enceladus from a refuelling somewhere around GTO. With stretched tanks and a transhipped payload the refuelling orbit wouldn't even need to be that high. So that gives 100t to an intercept. 4500m/s to a landing. Lander would probably need to have hypergolic propulsion with ~310s ISP. That'd take a large propellant fraction, but with 100t wet it's still probably 20t landed. Could do a lot with 20t landed.

Booster 3 completed ambient proof last night:

As stated earlier in the thread, the orbiter masses 75 tonnes dry and has an OMS ISP of 312s. With a bare bones Apollo style excursion lander payload weighing 15t (so that the orbiter remains in LLO) it would take about 340t of propellant to get to the moon and back, (assuming multi-pass aerobraking), 430t from LEO total That total is about 3.5 times the best mass to LEO STS ever achieved in service. It would need to be refuelled in orbit. The only craft capable of delivering hundreds of tonnes of propellant to LEO is Starship. Starship will be capable of going to the moon by itself *and landing* for a fraction of the cost of an STS launch. Starship is what Shuttle wishes it could have been.

3 equally spaced fins is the minimum for passive stability in both pitch and yaw. 4 is a simpler control scheme as pitch and yaw can be controlled independently.

I believe it's a sort of protective coating.

The extendable nozzle on some variants of RL10 isn't for altitude compensation, it's to reduce interstage length. Merlin 1D has an expansion ratio of just 16. It is the best kerolox booster engine ever designed. It has 7-19s more ISP than the F1, twice the TWR and nearly twice the thrust per unit area. If you slap a larger nozzle on it, not only would flow separation destroy it, but it would weigh more, have lower thrust per unit area, and, crucially, no longer fit in a cluster under an F9. Similarly RS25 has an expansion ratio of 69. To have an expansion ratio of 189 to extract full ISP it would need a significantly larger, heavier nozzle. As a hydrolox engine it already has woeful thrust for a booster engine (hence the SRBs), and the larger nozzle (assuming it survives flow separation issues) would cut its thrust per unit area by approx 2.5x and also reducing the number of engines you can fit under a notional stage by 2.5 times. RS25 SSTO isn't getting off the pad.

The idea of a stretched F9US is interesting! Likely an even better than its already incredible mass fraction. Even if it'll forever be on paper. I had thought they were at structural limits for length.

Glad to have been of help. :-)

It's this sort of revolutionary application that I'm most excited about!

Hard to tell without seeing your complete flight. As it's apparent gravity that the game states it will change depending on factors other than radial position, most notably tangential velocity. I'm a little defeated by the reason for the step change around full throttle, but the rest of the plot doesn't look too unusual. Maybe someone else will have some idea.

Centripetal acceleration is radius multiplied by angular velocity squared. Radius is 600,000m. Sidereal rotational period is 5h 59m 9.4s. Angular velocity is 0.0002914rad/s. Centripetal acceleration is therefore ~0.051m/s/s at the equator. Yup, that's the difference. The game is displaying "apparent gravity", not true gravity.

This formula checks out. In the limit where one object is very much larger than the second, gravitational acceleration is given by the gravitational parameter GM (also called mu) divided by the radial distance from the centre of the parent object squared, in the radially inward direction. And the radius of your position is Altitude plus Kerbin's Radius. I also agree that this calculates at ~9.80, 9.81ish using Kerbin's gravitational parameter and mean sea level (altitude 0). What might be happening is that apparent gravity at the equator is being reduced by the rotation of Kerbin. Give me as moment and I'll calculate that effect as well.

Well there probably is additional energy that *could* be extracted from kerolox using some monster full flow stage combustion cycle or similar. I don't have the numbers to hand, but it'd be a similar argument that the theoretical maximum for Hydrolox is around 530s for a stochiometric mix, so the 450s of RS25 and 465s of RL10 aren't 100% efficient. There are good reasons the theoretical maximum isn't *practically* acheivable, such as the 9GW required to turn the turbopumps in RS25, and back-pressure from the atmosphere. But suffice it to say, any advanced SSTO with technology that could put it on a par with *current* TSTO would be at least one and probably both of the following: 1) More expensive than a current TSTO due to advanced manufacturing techniques. 2) Incapable of matching a similarly advanced TSTO design.

Yikes

Then Stine is also wrong. Equating SSTO Vs TSTO for same DV: ISPc*g*ln((P1+SSTOw)/(P1+SSTOd) = ISP1*g*ln((P2+2Sw+1Sw)/(P2+2Sw+1Sd)) + ISP2*g*ln((P2+2Sw)/(P2+2Sd)) Where: ISP1 is 1st stage ISP. ISP2 is 2nd stage ISP ISPc is altitude compensating SSTO engine ISP with an average not exceeding ISP2. P1 is SSTO payload. P2 is TSTO payload. SSTOw/d is SSTO wet/dry masses. 1Sw/d is TSTO first stage wet/dry masses. 2Sw/d is TSTO second stage wet/dry masses. This has no solutions where the SSTO payload P1 is greater than the TSTO payload P2 for similar gross lift off weight and similar optimisation of engine performance and tank fraction.