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1. ## Earthrise from the lunar surface?

Excellent. Thank you very much. Bob Clark
2. ## Earthrise from the lunar surface?

This article suggests you will be able to see the full disk Earthrise from the lunar surface: Earth Rising Earth as seen from the Moon is always in the same place – true or false? It depends. By Paul D. Spudis MAY 15, 2014 https://www.airspacemag.com/daily-planet/earth-rising-180951474/ While most locations on the Moon's surface would only be able to see partial disk Earthrises, at the lunar terminator (separator between far side and near side of Moon) and at the lunar poles, you'll be able to see the full disk Earthrise. Anyone want to do a try in Kerbal Realism mode to show what this would look like? Intriguing question: will we see a "huge Earth illusion" like we see a "huge Moon illusion" when looking at the full disk? MOON ILLUSION IS ALL IN YOUR HEAD BY: BOB KING NOVEMBER 24, 2015 https://skyandtelescope.org/observing/moon-illusion-confusion11252015/ Bob Clark
3. ## Wow... Our Solar System Is HUGE

Right. Let me redo that calculation: Use equation x=1/2 a t2, and round off 1 g acceleration as 10 m/s2. Then 2x1016 m = (1/2)*10*t2. So t = 63x106 s. That's 730 days. The speed reached is v = at =10*63x106 = 630,000 km/s. This is double lightspeed of 300,000 km/s. Then you would have to consider relativistic effects. At some point as you approached light speed you would need to expend a huge amount of energy to maintain that speed, still without actually reaching lightspeed. Perhaps someone will do the calculation about how long it would appear to take for shipboard time compared to Earthtime for the journey. Bob Clark
4. ## Wow... Our Solar System Is HUGE

The time is actually shorter, and it doesn't quite reach light speed. It's surprising how fast and how far you can go by just 1 g acceleration: A nice way to remember the distance of a lightyear is that it's about 10 trillion km, which equals 1x1015 meters. Use equation x=1/2 a t2, and round off 1 g acceleration as 10 m/s2. Then 2x1015 m = (1/2)*10*t2. So t = 2x107. That's 231.5 days. The speed reached is v = at =10*2x107 = 200,000 km/s, less than lightspeed of 300,000 km/s. Bob Clark
5. ## Mars Rover Perseverance Discussion Thread

I would have loved to have seen a true microscope sent to Mars. After more than half a dozen landers there still has not been sent a true optical microscope sent. The best resolving power has been at no better than that of a geologists hand lens. This would have importance for the search for possible life, but also for geological samples. Bob Clark
6. ## Starhopper+Starship for heavy lift. Triple-cored Starship for superheavy lift.

Yes. They could use sea level engines for all six engines. You would lose on delta-v or payload though because you wouldn't get the high vacuum Isp of the vacuum engines. By the way, it is not well known that with altitude compensation you improve both sea level thrust and vacuum Isp for the sea level engines. So you would get better takeoff thrust actually than just 6 sea level engines. The vacuum Isp part is well known. But sea level thrust is also improved because sea level engines with fixed nozzles are a compromise. Even for sea level engines a large portion of the flight of that first stage takes place in near vacuum conditions. So to get good performance then also, you use larger than ideal nozzles for sea level. This decreases the sea level thrust. But with altitude compensation you make the nozzles adapt to ideal size both at sea level and vacuum and intermediate altitudes in between. I've been trying to get some Kerbal experts to do the calculation in Realism mode to see what the improvement is in payload or delta-v for engines given altitude compensation. It's not that difficult to do, really. For instance for just a standard fixed nozzle, if you want an accurate simulation you have to include how the thrust, so effective Isp, varies with altitude. Such variation has to be done with altitude compensation also; its just a different formula. The needed formulas are also well known. Just nobody has ever done it. My point is the improvement in payload with altitude compensation is quite high. For instance a rule-of-thumb among propulsion engineers is "every 10% increase in Isp results in 100% increase in payload." The reason of course is because of the exponential nature of the rocket equation. As Ray Kurzweil has noted, people really don't have a good intuitive sense of the nature of exponential growth. Most people would think "OK, so you improve the Isp 10%; so why would I spend this amount of money to increase payload 10%?" The issue is it is much better than 10%. A rough estimate I did was an increase of 25% for a two stage rocket. For a parallel staged rocket like the Falcon Heavy or the SLS, 40%. And for a SSTO, 100%. Because nobody has done an accurate simulation to see how payload is improved with alt.comp., nobody thinks it is worthwhile. Once you open yourself up to the possibility it might be useful it really doesn't take much thought to then come up with various different ways of doing it at low cost. Bob Clark
7. ## Starhopper+Starship for heavy lift. Triple-cored Starship for superheavy lift.

Elon on Twitter said hopefully the Starship will fly this week:https://www.cnet.com/google-amp/news/el ... -fly-soon/Presumably this will be a short hop test. But running the numbers the Starship could get a surprisingly high delta-v.The latest version has 3 level and 3 vacuum engines. Presumably only the 3 sea level ones will be used at launch. So this will mean 3 x 200 tons = 600 tons of launch thrust. I’ll take the propellant load as 400 tons to allow for payload at later tests. But launching the bare rocket could get 354*9.81Ln(1 + 400/120) = 5,100 m/s delta-v, past Mach 16.This though is the delta-v as an expendable. Some of the propellant has to be used though for landing so the actual delta-v achieved will be less than this.This scenario though illuminates the importance of achieving altitude compensation. Those 3 vacuum engines have to just stay idle during launch, like dead weight. Imagine instead having altitude compensation so all six engines could be used for liftoff. You would have 1,200 tons liftoff thrust. Nearly the full propellant load could be used. You would get in the range of 7,000 m/s delta-v. Actually it would be higher than this since the altitude compensation would also allow you to use the full vacuum Isp of the vacuum raptors of 380 s at high altitude. This would mean quite a large portion of the Earth could be covered by point-to-point rocket travel. This represents a huge market for the Starship.Bob Clark

9. ## Starhopper+Starship for heavy lift. Triple-cored Starship for superheavy lift.

The weight estimate is not new. It was the original weight estimate. How easy it would be is relative to taking another approach. The triple-core Falcon Heavy only cost 50% more in development cost than the Falcon 9 at triple the payload. In contrast, based on size, the 3 times larger SuperHeavy booster would cost 3 times more in development cost. Bob Clark
10. ## Starhopper+Starship for heavy lift. Triple-cored Starship for superheavy lift.

The increase in dry mass after the announcement of the addition of the movable wings was much discussed on the NasaSpaceflight.com forum. Prior to the new wings being added, Elon had said their specialty high-strength stainless steel version would require the same weight as the carbon fiber version. I agree it is puzzling why the increase would be that much. But there is precedent in movable wings being heavier as the example of the swing wing F-14 Tomcat shows. Bob Clark
11. ## Starhopper+Starship for heavy lift. Triple-cored Starship for superheavy lift.

No, I wasn’t referring to that larger diameter version, I think called the “Interplanetary Transport System”(ITS). I’m referring to essentially the current version but before the addition of the movable wings. It’s been much talked about on space oriented forums that the addition of the movable wings increased the Starship dry mass by approx. 50%, from 85 tons to 120 tons. I’m suggesting go back to the high mass ratio version. Then there are various options to get lightweight wings, landing gear, and thermal protection that would only subtract a proportionally small amount from the payload for reusability. Bob Clark