Monday, August 24, 2015

Neil Tyson -- Incompetent Ass

A little more fact and a little less fiction, please

At one time I was a Neil DeGrasse Tyson fan. Our culture needs more charismatic pop figures promoting science and rational thought.

But Tyson has a propensity for just making stuff up. A true devotee of science makes it a top priority to disseminate accurate info.

I'll give a few examples.

Tyson likes to promote space exploration -- that's a good thing. He also notes our space programs have generated spin off technologies that help the economy -- also a good thing. But he exaggerates and embellishes. Here Tyson credits the space program for miniaturizing electronics:

The urge to miniaturize electronics did not exist before the space program. I mean our grandparents had radios that was furniture in the living room. Nobody at the time was saying, "Gee, I want to carry that in my pocket" Which is a non-thought

Ummm….   No.

Making electronics more compact, less massive and less expensive was an extremely obvious thought. Tyson's statement is utterly ridiculous.

Tyson would do well to read Wikipedia's history of the transistor. There were efforts to replace vacuum tubes as early as the 1920's. TR-1, the first transistor radio, hit the market in November of 1954.

NASA was formed in 1958.

The Regency TR-1 transistor radio hit the market in 1954,
4 years before NASA was formed.

NASA and military aerospace have made substantial contributions to the development of electronics. For example, the funding of integrated circuits R & D. Let's crow about these real contributions. But please don't give our space program credit for the notion of miniaturizing electronics.

It damages our cause when someone like Tyson spouts complete B.S.. The tendency to exaggerate and embellish is one of the reasons space advocates suffer from a lack of credibility.

"He's an entertainer," Tyson defenders might say. "Embellishing the truth is standard practice to boost ratings. If he can recruit more supporters, who cares if he doesn't cross his t's and dot his i's?"  I didn't buy that but had to acknowledge the man has gathered a following. So I didn't grumble too loudly.

Then Tyson stepped over the line.

A malicious fabrication
(Just to be clear -- by "fabrication" I mean a made up story. Not necessarily with intent to deceive)


Like everyone else, I was horrified by the events of September 11, 2001. I braced myself for President Bush's reaction. I thought Bush would use the tragedy to demonize Muslims. Exploiting xenophobia is an all too common political device.

But Bush's response was a pleasant surprise:
The face of terror is not the true faith of Islam.  That's not what Islam is all about.  Islam is peace.  These terrorists don't represent peace.  They represent evil and war. 
When we think of Islam we think of a faith that brings comfort to a billion people around the world. Billions of people find comfort and solace and peace. And that's made brothers and sisters out of every race -- out of every race. 
America counts millions of Muslims amongst our citizens, and Muslims make an incredibly valuable contribution to our country. Muslims are doctors, lawyers, law professors, members of the military, entrepreneurs, shopkeepers, moms and dads. And they need to be treated with respect. In our anger and emotion, our fellow Americans must treat each other with respect.
What Speech did Tyson recall hearing after 9-11? He remembers Bush loosely quoting Genesis "Our God is the God who named the Stars". Tyson says he was "attempting to distinguish we from they".

Watching the Tyson's video I'm scratching my head. Bush wasn't trying to stir up hatred against Arabs, just the opposite. And where did this stuff about star names come from? Below is Tyson's rant. Tyson starts talking about Bush at around 1:30.

Bush did give a speech where he quotes Genesis saying God named the stars. But it wasn't a post 9-11 speech slamming Arabs. It was a eulogy for the astronauts killed in the Space Shuttle Columbia disaster.

From Bush's Columbia disaster speech:
In the skies today we saw destruction and tragedy. Yet farther than we can see, there is comfort and hope. In the words of the prophet Isaiah, "Lift your eyes and look to the heavens. Who created all these? He who brings out the starry hosts one by one and calls them each by name. Because of His great power, and mighty strength, not one of them is missing. 
The same Creator who names the stars also knows the names of the seven souls we mourn today. The crew of the shuttle Columbia did not return safely to Earth; yet we can pray that all are safely home. May God bless the grieving families. 
And may -- may God continue to bless America.
Somehow Tyson conflated Bush's Columbia disaster speech with post 9-11.

Chemically enhanced perception?

How on earth did Tyson manage to conflate 9-11 with the Space Shuttle Columbia disaster? I have a theory. Carl Sagan, Tyson's hero and mentor, was thought to indulge in a little weed now and then.

Perhaps Tyson has discovered psychotropic drugs can be used as a vehicle to explore other worlds and alternate realities. I'm not the only one speculating Tyson's a stoner.

Tyson's "Apology"

In a Facebook post Tyson admits conflating the two events. And he reposted this admission on July 1st, 2015. The more recent admission is still open to comments as of this writing.

Well, he makes the admission buried in the 10th paragraph. The first six paragraphs are devoted to glowing descriptions of Tyson's favorite subject: himself. The seventh paragraph he slams those petty and small minded "lawyers" who doubt Tyson's word. How dare they question his credibility just because they catch him in the act of making stuff up?

Here's Tyson's admission:
What followed fascinated me greatly.  As others had uncovered, the President indeed utter the following sentences: 
In the words of the prophet Isaiah, "Lift your eyes and look to the heavens. Who created all these? He who brings out the starry hosts one by one and calls them each by name. Because of his great power and mighty strength, not one of them is missing."  The same creator who names the stars also knows the names of the seven souls we mourn today. 
But I was wrong about when he said it.  It appears in his speech after the Columbia Shuttle disaster, eighteen months after September 11th 2001.  My bad.  And I here publicly apologize to the President for casting his quote in the context of contrasting religions rather than as a poetic reference to the lost souls of Columbia. I have no excuse for this, other than both events-- so close to one another -- upset me greatly.  In retrospect, I’m surprised I remembered any details from either of them.
This is all Tyson needed to say. Had his apology just consisted of these few paragraphs, he might have salvaged a little credibility.

But Tyson goes on to write:
Of course very little changes in that particular talk.
Utterly and completely wrong. As usual. That talk was about President Bush's idiocy. The whole Arabic star name thing was to "confound Bush's point". Sadly for Tyson, the point being confounded comes from an imaginary Bush that lives in Tyson's crack pipe.

And still more B.S. from Tyson:

I will still mention Islamic Extremists flying planes into building in the 21sth century. I will still contrast it with the Golden Age of Islam a millennium earlier. And I will still mention the President's quote. But instead, I will be the one contrasting what actually happened in the world with what the Bible says: The Arabs named the stars, not Yahweh.
Of course the Arabs named the stars. Does that falsify the passage from Isaiah? No. How does Tyson know God didn't name the Stars? God's existence or nonexistence isn't something that can be demonstrated with experimental evidence. His confident assertion isn't a testable hypothesis. It is beyond the purview of science.

But then again, Tyson's cult of personality has never been about science.

Saturday, August 8, 2015

Lunar pogo hopper

Paul Spudis recently offered some thoughts about Drones on the Moon. He notes conventional drones would not work on an airless world.

Spudis writes:
Sub-orbital “hops” (ballistic flights from point-to-point) are possible, but come at fairly high cost—it takes nearly as much energy to fly hundreds of kilometers on the Moon in a ballistic hop as it does to go into orbit and then descend elsewhere.
This is incorrect. Here I look at suborbital hops on airless worlds. A minimum energy ellipse going from point A to B would have a focus on the midpoint of the chord connecting A & B:

The other focus would be at the moon's center, of course.

The vis viva equation tells us
v=sqrt(GM(2/r - 1/a)

In this case GM is the moon's gravitational parameter, r is the moon's radius and a is the semi major axis of the ellipse.

Let's say A is 300 km from B. That'd be  about 9.9 degrees separation. Here's a pic:

.67 km/s to hop and another .67 km/s for a soft landing. For low lunar orbit that would be 1.68 km/s to take off and another 1.68 km/s to soft land. Energy goes with square of speed. (.67/1.68)2=.16. The energies differ by more than a factor of 6! How on earth did Spudis conclude these are nearly the same?

Here is my Lunar Hopper spreadsheet. There's a tinted cell user can input distance between point A and B. This is the first document I've uploaded to Google docs, hope it works.

Spudis suggests spherical pit bots for lunar drones. These bots use micro thrusters to hop and hover. Whether the hop is 5 meters or 500 kilometers, the most efficient hop is the minimum energy ellipse described above. On the moon a ten minute hover costs about one km/s delta V. Spudis justifiably grouses about the tyranny of the rocket equation. But these pit bots rely on reaction mass to move. They don't circumvent said tyranny.

Pogo Hoppers

Various folks talk about lunar drones at Spudis' forum. Someone who goes by the name finkh mentioned pogo sticks. An interesting notion, in my opinion.

When I was a kid, my pogo stick used a spring. Solar cells might provide energy over time to compress a spring, thus avoiding the use of reaction mass. No more nasty rocket equation! On landing the spring absorbs the impact. The compression on impact might be a way to recover some energy.

I moved over a variety of terrains with my pogo stick. I could move forward, backward, left or right. It seems feasible to develop a robot with similar abilities.

But as I recall, getting from point A to B on a pogo stick was more strenuous that walking. So I'm not sure compressing a spring on impact is a great way to regain energy. Looking at existing robots like Big Dog, it looks like powerful engines are needed to power the device. Once again, the need for a better Alpha rears its ugly head. Elon Musk seems to be working on improved solar panels and energy storage. Hopefully Tesla Motor's R&D will have applications in space exploration.

How much impact can a pogo stick take? The 300 km hop pictured above hits the ground at .67 km/s or about 1500 miles per hour. No, I wouldn't want to be on that pogo stick.

This list of pogo stick records says Biff Hutchison jumped nearly 3 meters high. By my arithmetic he hit the ground at about 7.5 meters/sec or about 17 miles per hour.

Assuming 17 miles per hour is maximum jumping and landing velocity, a lunar pogo could jump about 36 meters (assuming the hop was a minimum energy ellipse from point A to B). This hop would be about 9 meters high.

A jump 36 meters long and 9 meters high isn't spectacular but such a device might have uses. And I like the image of a pogo stick on the moon.

Friday, August 7, 2015

A new tether spreadsheet

A few notes on my old spreadsheets

Up to now, most of my spreadsheets for vertical tethers and elevators have been based on Jerome Pearson's work. The taper ratio I've used is based on equation (10) from Pearson's The orbital tower: a spacecraft launcher using the Earth's rotational energy. A screen capture from Pearson's PDF:

Pearson is looking at a very specific vertical tether here, a space elevator whose foot is at earth's surface (r0) and whose balance point is at geosynchronous orbit (rs).

But I make some substitutions to make Pearson's equations more general:

Substitute r0 with rfoot, the distance of the tether's foot from body center. 

Substitute rs with rbalance. By rbalance I mean the point on a vertical tether where centrifugal acceleration exactly balances gravity.

Substitute g0 with gfoot. By gfoot I mean gravity at tether foot. Pearson sets g0 at 9.8 meters/sec2, earth surface gravity. I set gfoot as G*(mass of central body) /  rfoot 2.

My resulting spreadsheets were cumbersome and complicated. I don't like complicated -- more opportunities for error. And indeed my early versions had many errors that gave obviously wrong results. Through careful proofreading and many bottles of aspirin I started to get numbers that matched Pearson's. But I remain uncomfortable with these sheets.

A new tether spreadsheet

Then Chris Wolfe sent me his Phobos tether spreadsheet. Chris' approach is simple and straightforward.

First he figures payload force at the tether foot: payload mass*net acceleration. In the linked spreadsheet, net acceleration is Mars gravity - centrifugal acceleration - Phobos gravity. Given the tensile strength of the tether material, this sets tether cross sectional area at the foot. Setting a safety factor of two will double this cross sectional area.

Then to the payload force he adds the force exerted by the length of tether just above the payload: density * cross sectional area * dr * net acceleration. This sets the cross sectional area of the next short length of tether. Again, the safety factor number multiplies this cell.

And so on up to the balance point.

Summing the mass of these cylinders gives a very good approximation of tether mass.

I had used a similar approach for calculating tether mass:

Tether mass is tether density times an integral giving tether volume from foot to balance point. For cross sectional area I used Pearson's equation 9 (see top of page). Being unable to solve the integral analytically, I chopped the tether into many small lengths and did a Riemann sum. In other words my numeric method for calculating mass is nearly identical to Wolfe's. Except Wolfe has a simple and straightforward method of getting the cross sectional area. 

The numbers from my spreadsheets closely match Wolfe's which also seem to match numbers from credible folks like Pearson or Aravind.

Chris' method is more versatile. A few advantages:

We can look at mass of decoupled upper tether length

If you have a huge anchor mass (like Phobos), the upper length becomes decoupled from the lower. The need to balance newtons from above with newtons from below is no longer an issue when anchor mass is 1.07e16 kg. 

If the upper length is independent of the lower, gravity at the tether foot isn't relevant. But Pearson's methods make heavy use of h, the tether material's characteristic length at the tether foot. This characteristic length has  gfoot in the denominator.

With Wolfe's method we can ditch the irrelevant h. Just as with the foot, we can start with net newtons at the tether top and then work our way down to the balance point.

We can look at moon tethers balanced from L1 or L2

Pearson's elevator model assumes two accelerations, earth's gravity and centrifugal acceleration. Wolfe's model can easily include a moon's gravity in the net acceleration. I am looking forward to tweaking Wolfe's spreadsheet to look at lunar elevators from EML1 and EML2.

More to come

Chris Wolfe's tether model enables me to scrutinize many of my favorite scenarios in more detail.

Besides this wonderful spreadsheet, Chris sent me a lot of other neat stuff. As time and energy allow, I'll use his ideas as the basis of drawings and discussions.

August 8 edit: Chris Wolfe has started a new blog Bootstrapping Space. I am predicting it will be an increasingly valuable resource as time goes by.