True! Short thread 🧵

First, this article is an example from 2017 of NASA stating that NASA budgets are not enough to do Mars missions: arstechnica.com/science/2017/0…
(2) An example from 2013, former NASA Admin Bolden explaining that NASA cannot afford to do Mars missions because it can only afford to build SLS and Orion. It cannot afford transfer vehicles, landers, Mars habitat & power systems, ascent vehicle, etc. spacenews.com/37808bolden-ca…
(3) The Agency finally realized and admitted in the mid 2010s that it needed to develop a new economic strategy if it wanted to ever get to Mars. It did, & called the strategy “Sustainable Exploration.” It had about 10 bullet points, including the following ideas...
(4) One idea was to keep building up infrastructure in space so there is always a net gain.

Another idea was to develop building blocks over time (SLS, Orion, later some others).

But another idea relevant to the recent flights of billionaires in space was THIS: ...
5/ The Agency would begin encouraging private industry to develop commercial businesses in space, so THEY would sustain the in-space building blocks using their OWN revenues which would not come from NASA! Here are some examples of the Agency saying this: ...
6/ This quote is from Gary Martin, who was head of the Partnerships Program at NASA Ames. From: catalog.libraries.psu.edu/catalog/159946…
7/ These examples showing the new & growing reliance on commercial space are from a NASA document “Voyages:
Charting the Course for Sustainable Human Space Exploration” nasa.gov/pdf/657307main…
8/ A few more examples from that document. Note how commercial space is being treated as a “partner” similar to the international partners (European Space Agency). These are not mere contractors, but businesses that have their *own* activities in space besides supporting NASA.
9/ I attended some workshops where NASA explicitly discussed how these commercial companies need to create revenues from commercial activity so they aren’t getting all their money from NASA, otherwise it is just a shell game.
10/ An example from a NASA website: “...public-private partnerships...stimulating commercial activities...”
nasa.gov/topics/moon-to…
11/ And the most recent example, the source selection document for the NASA Human [Lunar] Landing System. SpaceX was praised for having a well developed plan to create commercial revenue with its lunar lander. This was a major factor in NASA’s evaluation. nasa.gov/sites/default/…
12/ To summarize: NASA has a strategy that relies on commercial companies developing strategies to create *profit* by doing things in space *other* than supporting NASA. There is no other way for NASA to reach Mars and do the other great exploration we want it to do. So...
13/ NASA now has a number of programs specifically designed to help develop these commercial companies so NASA can benefit from the synergy. Commercial Cargo, Commercial Crew, Lunar CATALYST, Commercial Lunar Payload Services (CLPS), and the Human Lander System.
14/ Now it is tricky, finding ways to profit in space apart from just supporting NASA or just putting up satellites. (I have kept a list of concepts for many years.) Space Tourism is one of the ideas. We argue how scalable it will be. Will it only have billionaire customers?
15/ Most people believe it will be scalable at least to some degree, the costs dropping over time creating a large growth in ticket sales. We think it will include trips around the Moon, to the lunar surface, & beyond. But will it have enough synergy to really help NASA?
16/ People disagree over this, but as in all business the proof is in the pudding. I have changed views over the years. I now think it *will* grow to be very significant. In any case, it will be a non-negligible part of the revenues in the portfolio of many space companies.
17/ And the tech to do space tourism is common with the tech for other space activities, so the synergy is not just between commercial space and NASA, but also between multiple commercial activities.
18/ Other commercial space activities include mining water on asteroids and the Moon to boost commercial communication satellites and support other non-NASA transportation. We can provide that water to “gas stations in space”. orbitfab.space
19/ My own list has about 39 commercial space ideas on it, some crazy, some very very real. Space entrepreneurs are creating many other business concepts. Space tourism is just the beginning. Something I’ve worked on: nasa.gov/directorates/s…
20/ So to reiterate, these commercial space activities are deeply embedded in NASA’s plan for Solar System exploration. They are not a distraction. They are the plan. Billionaires flying into space is part of the process of companies creating their success so NASA can do more.

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More from @DrPhiltill

15 Jul
I agree with the piece on this: there are risks as we enter space. We must solve them! But IMO the piece is not a real ethics argument since it weighs only risks, not benefits, & the arguments fall short of justifying th claim that forcing ppl to stay on Earth is pragmatic & good
I would argue it this way instead: we can't pragmatically keep the cat in the box (considering global realpolitik) even if it were good to do so. But it isn't good to do so, becoz the benefits vastly outweigh the risks & becoz the risks are inherently solvable. Therefore,...
...the best way forward--indeed the only pragmatic way forward--is for nations that value ethics (as imperfect as we are) to do the *best we can* in leading ethically and proactively, so we are operating from the best possible position to create a good outcome. But that means...
Read 10 tweets
11 Jul
I might as well dive into the other argument, too. Kármán Line vs. 50 miles up. Where does space begin?

Well let’s start by saying the Kármán line is based on a silly thought experiment so it provides no real basis to define the limit of space. It means nothing and is silly.
2/ The Kármán altitude is based on how fast a vehicle has to travel to produce enough aerodynamic lift on its wings to support its weight. It depends on how thin the atmosphere is. The higher you go, the thinner the air, so the faster you must move to use wings to stay up. But...
3/ If you go fast enough, then ignoring atmospheric drag you would not need wings at all because you’d be in orbit. So the height where the required speed to use wings is the same as the speed if there were no air — that is the Kármán altitude. But.../
Read 10 tweets
11 May
A paper just came out analyzing rocket exhaust blowing lunar soil. It is important for at least 2 reasons. 1/n

Reference: Chinnapan et al., "Modeling of dusty gas flows due to plume impingement on a lunar surface," Physics of Fluids 33, 053307 (2021) aip.scitation.org/doi/full/10.10….
2/n First, there is great uncertainty in how *fast* the lunar dust goes. It is hard to model rocket exhaust physics on the Moon because fluid flow equations break down as the gas spreads into vacuum. The relevant equation is the Navier-Stokes equation. (screenshot from Wikipedia)
3/n In that equation, the constant μ is gas viscosity. It is not really a fundamental thing in nature. It was invented by averaging lots of molecules bouncing in a small volume of space. It tells us how much the momentum from one volume diffuses into nearby volumes.
Read 14 tweets
8 May
I love this quote for so many reasons, I’m going to translate it into a modern writing style. 1/n
“It used to be there weren’t many people bold enough to cross the ocean, but now it’s so easy even fearful and faint-hearted people can cross it. So maybe someone will invent a way to travel to the Moon, even though it seems like such a terrible voyage across vast, empty sky! /2
[I’m translating a mix of two versions of his book to get his entire thought.]

“And without a doubt there will be bold people to take that venture, just like crossing the sea!

You might be thinking we have no way to sail into the sky, unless the poet’s fantasies were true.

/3
Read 9 tweets
7 May
What I find cool about successfully hearing this sound isn't just the low density of the atmosphere, but also the fact that the atmosphere is almost pure carbon dioxide. CO2 is unusual among gases for having very high bulk viscosity, which vastly reduces sound propagation.
2/ Viscosity tells how momentum diffuses through a gas. Honey has high shear viscosity, meaning if flows slowly. Water has low shear viscosity, so it flows easily. In addition to shear viscosity, there is the lesser-known "bulk viscosity" related to the rotation of molecules.
3/ In most gases, the bulk viscosity is ~ zero, but in carbon dioxide the bulk viscosity κ is 1000 times greater than the shear viscosity η. The attenuation of sound is described by this equation. So (order of magnitude) sound attenuates about 1000x more on Mars than on Earth.
Read 4 tweets
21 Apr
From the talk I gave at the ASCE Earth & Space conference today. When you land on the Moon, your rocket exhaust is faster than lunar escape velocity and there is no atmosphere to slow down the dust you blow. We need to worry about damaging things in orbit.

Short thread... /1
We've done a lot of experimental work to understand how much lunar soil will blow because of the rocket exhaust during a landing. The work included reduced gravity flights measuring soil erosion in lunar gravity. /2
As you would expect, erosion rate is faster when gravity is lower. That part of the physics is easily understood, at least. Erosion of soil on another planet scales as 1-over-gravity. /3
Read 9 tweets

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