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Q&A Section / Re: Apollo Q&A
« Last post by GClark on Today at 06:43 AM »
"Hey, Dick!  I fell asleep!"

"zzz...Huh, what?"
New Physics for Space Technology / Re: Useful Skepticism
« Last post by ppnl on Today at 06:42 AM »
The EMDrive is a free energy device.

No it isn't. It may tap into a new as yet unused energy reservoir.

A valve that opens the waterflow from a dam into a turbine/generator set is not a free energy device if it takes less energy to operate than the generator produces.

That is true. But that will require fundamentally new physics. The entire body of physical knowledge places serious constraints on any such new physics. But in principle it could be done.

But my Bayesian priors...
New Physics for Space Technology / Re: Useful Skepticism
« Last post by ppnl on Today at 06:34 AM »

I mean that thee is no propellant expelled.

The earth itself is the propellant. Because you are dealing with angular momentum here the earth isn't expelled but only spun up in the opposite direction by a very small amount.

It doesn't lose mass to increase its velocity.  (like other propellant-less systems) It could use a motor instead of a hand and a force sensitive computer to do the torquing and the power could come from solar panels.

Only if you mechanically connect the motor to the ground. Without that connection it cannot push against the earth (Its propellant) and the motor will end up rotating around the grip handle in the other direction. The device itself will spin but only slowly because most of the energy will be pumped into the electric motor spinning the other way. [/quote]

A similar idea was proposed with the EM drive and it was stated that if the EM drive could increase the spin that at a particular velocity it would become over unity I think either because it wasn't expelling mass or it was claimed a constant force of thrust.

But what are you pushing against? Unless you can point to something you are pushing against you seem to be violating conservation of momentum. Well maybe there is something that it is reacting against but you have to be careful how you do it or like Shawyer you will break all logic. Cats liveing with dogs... do you really want to see the horror?

There were arguments against there being a constant force for thrust.

Not sure which device you are talking about here. Constant force should always produce constant acceleration. But you need ever increasing power to to provide constant force. For example consider a car engine producing constant power. The faster the car goes the slower it will accelerate until its acceleration becomes undetectable.

Such an old post on the EM drive thread I am not sure where to find it again.  Later arguments more recent were that for a photon drive (laser) that it becomes over unity at the speed of light.  This device would obviously provide more torque than a laser.  I would agree it is just a power storage device and doubt that it would become over-unity.  Obviously it should take 4 times the energy to double the velocity at lower velocities.  1/2m(2*v)^2=4*E.  So why not the same for a rotating EM drive if it works?

In order to see if it is over unity we have to know what it is using for propellant. If constant power produces constant acceleration then it is over unity no matter how you look at it. Even if you require the power to increase to provide constant acceleration You still have a problem with Galilean relativity. In order to see how much power is needed to accelerate we need to know the relative motion of you and the thing you are pushing against (your propellant) is.

Imagine an electric car coasting across a flat plain at some unknown velocity. How could you tell how fast you were going? Simple, feed some set amount of power into your motor and measure how much you accelerate. But what if you are going backwards? Now to decelerate (just accelerating in a different direction) you just feed the rotation of your tires backward to use your motor as a generator and get power.

If that thing that the emdrive or whatever is pushing against is moving really fast then it will not be of much use as a drive because it would require far to much power. It maybe useful as an energy source and until you identify what it is reacting against it will appear to be an over unity device.   
SpaceX Mars / Re: The costs associated with SpaceX's Mars Ambitions
« Last post by MP99 on Today at 06:28 AM »
I tend not to think of Mars as being a cash economy, but there will be some need to manage scarce resources such as Earth / Mars bandwidth.

In this case, perhaps it could be managed via quotas rather than charging.

Cheers, Martin
Orion and Exploration Vehicles / Re: Orion Discussion Thread 2
« Last post by woods170 on Today at 06:24 AM »
Well, guess what: that's exactly what led to the Apollo CSM backshell being taped with strips of metallic-coated Kapton.
So, my guess is that a (Kapton?) film will be applied over the backshell TPS, much like was done on the Apollo CSM. It will burn-off easily upon re-entry with the remains being easily removable in support of post-flight assessment of the condition of the TPS.
Actually, the metallic coating on the Apollo CSM didn't just all burn up on reentry. Remember, this is the back-shell, so the thermal environment is orders of magnitude less intense than the heatshield itself. I attached a picture of Apollo 8 after it came back from the Moon. Kapton film still clinging to the spacecraft.

Honestly, I think those black TPS tiles are WAAAAYYY overkill for the whole backshell when just some kapton film seems to survive at least to some degree. They would be better off with just a thin bit of ablative material or something over most of the backshell, IMHO. Heck, they could probably do alright with some white tiles or blankets over most of the backshell.

Bad example. Take a look at some of the images of Apollo lunar missions showing the 'wind' side of the backshell (image below of Apollo 11, 13, 14, 16, 17): most, if not all, of the Kapton gone (burned off) and degradation of the underlying TPS.
Remember, the backshell still sees very high temperatures despite them being an order of magnitude less than the primary heatshield does.

Also, the black TPS tiles are a carry-over from a previous program and do the job just fine. Particularly given that the CSM was originally designed to be reusable and the fact that the backshell TPS holds a secondary role of MMOD protection. It might sound counter-intuitive but those TPS tiles-on-a-carrier-plate do a better job as MMOD protection than does the Apollo-style ablative material.
SpaceX Mars / Re: The costs associated with SpaceX's Mars Ambitions
« Last post by MP99 on Today at 06:18 AM »

You're talking 3 satellites produced every day...

Implication:- eventually, they'll be disposing of three sats per day, too.

I wonder whether that will noticeably increase public sightings of sat reentries?

Cheers, Martin
Orion and Exploration Vehicles / Re: Orion Discussion Thread 2
« Last post by woods170 on Today at 06:18 AM »
Carrying this over from the SLS thread as that one had gone OT:

Guaranteed it wouldn't be cheaper. It never is. We're not saving money on the Orion service module being done by Europe, because there's huge overhead trying to communicate across continents and across language barriers, unit barriers, protocol barriers, cultural barriers. The only "advantage" is that it makes Orion much harder to cancel.

Well, the overall effort doesn't cost less, but the amount the U.S. has to pay overall is less because the Europeans are picking up the Service Module portion of the Orion (or at least a major part of it)....
Nope. It doesn't save the US money. Remember, we already half-had a design for the service module. We're still doing the overall engineering for Orion. We're also supplying ESA with many of the service module parts.

...I guarantee we aren't saving money with this. It's just to keep Orion from being canceled.
The US is indeed supplying ESA with parts for the ESM. But neither many, nor for free. Most parts of US origin (such as avionics components) are bought from US suppliers by the ESM main-contractor (Airbus). That includes the 8 auxilliary engines. Just about the only major component given to ESA 'for free' is the OMS engine.
There is no sense in selling the OMS engine to ESA/Airbus given that they are surplus items from the STS program.

The actual reason for ESM still costing the US a lot of money is the additional testing and certification and integration efforts involved. In stead of relying on ESA to do ALL testing and certification and integration for them, NASA has decided to do a major portion of the testing, just about all of the certification, and most of the integration (with the crew module) activities themselves.

Simply designing, developing, basic testing and building the ESM is not really where all the money is spent. Particularly not given that many of the ESM systems and components are direct descendants from ATV systems and components. It explains why the ESA-cost for ESM is well below Euro 500 million. The really expensive activities involved with ESM are still being done by the US.
Please, take any further discussion about Orion and ESM to the appropriate threads at the Orion section. Thank you.
X-vu, Y-vu Z-vu  are viewing the 3D lattice in the x, y, and z directions and so looking at the y,z plane, the x,z plane and the x,y plane where z is the axis of rotation of the cavity, the two sources are along the x axis and y completes the right hand coordinate system. The EM field has 6 vector components, three electric, ex, ey, ez and three magnetic, hx, hy, and hz.

One would think that by looking at the ex, hx vector component from the other coordinate directions, that there would be nothing to see. That does not seem to be the case. It would be helpful if there were an easy way to visually compare the energy levels across all of the 18 (24 because there are two slices in the x,y plane, BEZ and SEZ) slices but that is a surprisingly difficult challenge.
Given that the title of this thread concerns planetary/science missions, I'll extend the booklist into the latter:

- The very first light, by John C. Mather and John Boslough, about the Cosmic Background Explorer (COBE) mission.
- Ripples in the Cosmos, by Micheal Rowan-Robinson. This details the impact on cosmology by the Infrared Astronomical Satellite (IRAS) and COBE missions. Details some of the struggles in getting both IRAS and COBE off the ground.
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