Monday, December 8, 2014

Sunday, January 5, 2014

The year in review and Propulsion Physics

Wishing everyone all the best for 2014, clear skies and smooth waters. 

Finished all my studies in marine engineering (I did get my next Chief Engineer's licence) and I'm back into Physics. Thought it would be interesting to look at 2013 in hindsight and sum up where we are up to. To be clear here I am looking at alternatives to chemical rockets for propulsion purposes in getting hardware from ground to Low Earth Orbit. As previously noted, this is a make or break issue for long term manned deep space exploration including interstellar travel.

There are plenty of studies looking at the Physics in getting hardware light-years from Earth however few that look at how to get hardware 100Km or so into orbit without using chemical rockets. Most of the interstellar related propulsion studies I've seen don't have applications for at least 100 years, although interesting they demand a fusion or other high energy shipboard power plant or an extensive beamed power source. The solar sail solution is elegant however past Jupiter's orbit is somewhat less effective because of the diminished solar radiation intensity and the very large sail area looks very impractical. They also don't address how the starship will be built in the first place and presumably assume an extensive space based shipyard / infrastructure. To sum up all the current starship designs proposed for interstellar travel have major problems, are impractical for interstellar travel and the cost would be astronomical, although the physics is sound. So there's still a lot more work to be done in this area before man is ready to launch an interstellar starship to other star systems.

An alternative propulsion system to chemical rockets on the other hand is achievable within a more reasonable time frame (say 30 years). The space elevator is feasible although considerable progress in the fabrication of carbon nanotube fibres has to be achieved before this gets anywhere near to reality (apart from the large dollar investment).

The space elevator concept. Image: Space Elevator Wiki
Gravity Control Propulsion (GCP) would be another logical (more elegant) alternative however the underlying Physics of General Relativity (GR) still hasn't been worked out. Until this is understood the viability of GCP cannot be answered (although the basic requirements from GR have been established). The validity of the current alternative models to GR are not yet clear. Most of the models that I have looked at don't even attempt to come up with predictions that can be verified by experiment today. It is also not clear why some areas of research in Physics concentrate on finding a unified model of physics in quantum gravity as Nature has not made this a clear requirement.

A basic requirement for GCP: a flat spacetime metric within a curved gravity well. Image: CI
Are there any other viable alternatives? Unfortunetly the other options such as electromagnetic catapult launches, tethered pendulums from orbit, external nuclear pulse propulsion etc are also problematic to say the least, again requiring either considerable infrastructure, radiation fallout, extremely high costs or payload launching capability is so small that we might as well continue to use chemical rockets which are at least affordable for small payloads until an elegant solution is found. We'll see what 2014 has to bring for Propulsion Physics.

CI.

Chemical rockets, the only means today to get into orbit. Image: NASA.

Thursday, October 31, 2013

Nuts and Bolts 31/10/13

Haven't done much Physics the last 2 months or so, been too busy with a Marine Engineering course I'm doing at the Hunter Institute - TAFE at Newcastle, this is towards getting my next Chief Engineer's licence. Some random photos below of the marine engineering workshop, Newcastle and the maritime action on the busy harbour (click for bigger versions). Impressive fleet of tugboats they have there. The wineyards up the Hunter Valley are also worth a visit.
 
 
                  
 

Tuesday, August 27, 2013

Is Gravity Control Propulsion viable? Part 6

Thought I might have some fun, I was thinking on some of the questions Marc Millis asked in his talk on Space Drives and Gravity Control Propulsion and it is useful to address his questions from the point of view of the model currently being worked on to see if there are any major logical inconsistencies with current Physics and if so why and if they can be addressed. Several screen grabs from Marc's talk are shown below to address the questions put forward. Note that I am answering the questions with the modified EMQG model in mind (which at this stage remember is a hypothesis which may have errors) however here we go.

Luke's Landspeeder (from the Star Wars fictional movie) has the ability to levitate above the ground and has some kind of jet engines to propel it forward. Will the frog get squeeshed if the speeder went over it?


No. The frog will become weightless while it is in the speeder's volume of influence on the local spacetime metric so the frog should survive. If the speeder parked above the frog, the frog would just be floating underneath the speeder as if it was in a space station in orbit. As the speeder approaches the frog, part of the frog's body will have weight and the other part will feel weightless which might confuse the frog for a moment (interestingly enough levitating a live frog on Earth has been done in the lab via different means: direct diamagnetic levitation). Note that Luke and C3PO will also feel weightless inside the speeder but a bird flying above the speeder outside the volume of influence will need to fly as normal to stop falling towards the ground.

What will happen to the speeder when it encounters the obstacles forward? It will clear the smaller ones but will crash into the higher ones unless Luke makes an altitude adjustment to the speeder. The GCP field of influence will act on the local spacetime metric causing objects to become weightless within, this may be a problem obstruction wise with loose objects if there are other influences involved such as wind etc. 


Which path will the speeder follow across the cliff? The green path, the speeder will go straight across as if there was no cliff at all. 

When the speeder is parked will it shoot off if pushed? (it appears rigid in the movie when parked). Momentum is conserved, there is no difference pushing the speeder in free space or at ground level when parked, it will drift away slowly, when parked the speeder will have to use an anchor of some kind or turn the vehicle off once on ground.



Ok so here is a list of GCP approaches Marc puts up and I've crossed out the ones which I think are either incorrect or unviable:
  • Zero out gravity of the vehicle? 
  • Zero out surrounding gravity?
  • Antigravity?
  • Force fields on space itself? Yes but depends on what is meant by "force fields" and "space" however this is the closest option which would agree with the model. Although the first two in the list regarding zeroing out gravity can be net effects they are incorrect because we cannot "zero out" the background accelerating virtual fermion field. Note that inertia is also not "zeroed out" in this process.
  • Shield gravity?
  • Ground repulsed?



The problem of providing a gravity earth-like environment in a starship (without relying on spinning structures or linear acceleration) can be reworded as: the flat spacetime metric inside the starship needs to be curved locally since gravity is curved spacetime. This is assuming the starship is in deep space, stopped and far away from a gravity well.

As far as keeping the artificial gravity net acceleration 1g inside the starship constant for the crew, the situation gets complicated if the starship is in orbit around a planet, undergoes manoeuvres ie accelerations, changes in altitude, course corrections etc. Speculating here, a super fast computer would have to evaluate the exterior spacetime metric curvature in real time and compensate the metric curvature inside the starship accordingly all this while taking into account the starship's own accelerations. It should be noted that there is no such thing as a pure flat spacetime metric anywhere in the Universe, however for discussion purposes far away from large masses it is a close approximation.

I haven't looked into this however it is quite feasible if the model allows one to change a curved spacetime metric to a flat metric then following symmetry principles in Physics, a flat spacetime can be curved artificially (not by using mass or energy-density as done by Nature). So in other words an acceleration needs to be imparted to the local virtual fermion particle field to obtain a net effect of curved spacetime which would result in local artificial gravity in the starship equivalent to natural gravity at ground level on Earth.


According to the model, Mach's Principle (and all the variants) is incorrect. Local physics is not determined by the large scale structure of the Universe. The large scale mass distribution of the Universe determines the widescale spacetime metric structure but within the spacetime metric inertia is purely a local quantum effect. The starship in the above slide is not pushing "against the mass of the Universe" but locally. As we'll see the model shows no inconsistencies with the Equivalence Principle which is an important test however other subtle problems are run into which will be explored in the upcoming paper I'm working on titled "A quantum model of spacetime metrics".

All in all an interesting talk by Marc, this is the last post on these GCP part series. The 100 Year Starship Symposium is coming up next month hopefully they'll have videos on the talks as well.

CI.

Sunday, August 25, 2013

Ship spotting Sunday

Well after a few hours flattening spacetime metrics ;-) I went for a walk this early evening and spotted Carnival Spirit in Circular Quay. She's a decent size passenger ship, only departed half an hour or so later after I took the photo.

Carnival Spirit getting ready to depart Circular Quay. Photo: CI.

Tuesday, August 20, 2013

Comments on Starship Congress 2013

I hope that video streaming for future interstellar conferences will be standard as I suspect many people outside the US can't attend. Some comments which came to mind after watching the videos:


  • Not much was said about the space radiation problem for humans (it is estimated a human can only survive up to 2 to 3 years in space in a standard spacecraft). This problem will have to be solved before long human deep space missions are considered. Otherwise probes will continue to do most exploring for us for the foreseeable future. Even a trip to Mars several months long poses a radiation health issue for the crew. The passive and active shield systems for the spacecraft will have to protect at least the human habitat in the spacecraft from dangerous space radiation and bring it down to at least 30mSv/year (workplace maximum radiation dose standard). At sea level, cosmic radiation exposure is 0.3mSv/year, at an altitude of 3Km it is 1.2mSv/year in Europe. There is a rundown on the problem discussed here. For any future manned interstellar mission (including deep solar system) this is a high priority research topic.
  • As mentioned previously in this blog, it is unlikely interstellar travel will kickoff unless a replacement for chemical rockets is found to place hardware from ground to Low Earth Orbit. The expected large amount of hardware required for interstellar missions will make the cost too prohibitive. So although it is interesting to discuss interstellar missions which most likely won't happen for at least another 50-100 years, unless the more pressing problems are solved first, it is unlikely there will be interstellar missions for a very long time. Space Drives or Gravity Control Propulsion would be a game changer, this should be another high priority research topic. Even if a space elevator is built here on Earth, it doesn't solve the problem for Low Planetary Orbit to ground and vice versa transfers on other planets.
  • Warp Drives and Wormholes: as mentioned previously these are allowed in General Relativity only but denied by Quantum Physics. Experiments related to these will continue to yield negative results. General Relativity is a classical model of the background dynamic quantum vacuum which works very well at describing Nature however the research so far hasn't shown how Quantum Physics would allow warp drives and wormholes to be physically possible.

CI. 

Update: There's an interesting wiki article as well on the space radiation issue worth a read: Health threat from cosmic rays.

Update: The Space Elevator Conference is on at the moment in Seattle. Last time I checked the state of the art fabrication process could only make carbon nano tube fibres a few centimetres long in the lab. These fibres need to be yarned into a cable long enough to reach geosynchronous orbit for the space elevator tether. A steel cable doesn't have enough tensile strength and at a length of 35786 Km will just break. Interesting to keep an eye where they are up to. To me this is Plan B if Space Drives or GCP turn out to be unviable because space elevators require a considerable amount of infrastructure to work while a hypothetical GCP enabled ship would not and would be free to manoeuvre around a planet (a big advantage). Also keep an eye out for the Skylon Project (Plan C), cargo transport is limited but the vehicle itself is quite neat and is really a big improvement over the Space Shuttle if they can get it working. The space elevator and the Skylon Project (not quite) are currently the only viable alternatives to chemical rockets regarding getting hardware into orbit from Earth that are feasible. 

Sunday, August 18, 2013

Starship Congress 2013

Starship Congress 2013 is on at the moment in Dallas. There was an interesting talk by Marc Millis on Day 3 regarding Space Drives.


CI.