The Spaceward Foundation

When?

How close is the Space Elevator? How expensive will it be?

The Plan

Technically speaking, the Space Elevator requires two major achievements: a tether which is at least 30 GPa-cc/g strong (see below), and a long-range power beaming system in the Mega-Watt range.

We define phase 0 as demonstrating these two technological building blocks, and we plan to do this by the year 2010, including a 10 GPa-cc/g CNT tether, and a multi-kWatt km-scale power beaming demonstration.

With these benchmarks demonstrated, we plan to pursue a 5-year development phase (phase 1) of full-performance components, followed by a 5-year system development effort (phase 2). This puts the beginning of construction (phase 3) around the year 2020.

The cost of phase 0 is well under 5 million dollars, and some of it is being achieved by the Elevator:2010 challenge project for significantly less than that. Based on current results and publications, we believe the objectives are very much achievable. (The results of phase 0, btw, are very much commercially viable, and we plan to use them to fund phase 1)

Phase 1 is the highest-risk portion of the development plan, since it aims to achieve the largest advance in performance. We estimate the cost of this researcg phase at under 200 million dollars, and it will result in removing any doubt about the feasibility of the SE project - by far the most important milestone in the plan.

Phase 2 is the main design phase - 5 years to design every nut and bolt on the anchor station, the climbers, the deployment systems... This is an aerospace design phase not much different than designing a new type of airplane or space capsule. The cost of this phase is much higher, and it will be performed by subcontracting to major aerospace companies.

Phase 3 is a direct continuation of phase 2, including the building of the ground infrastructure, the full length ribbon, the power beaming station...

All in all, we estimate the entire program to cost less the $10B - a small amount compared to the development and construction costs of programs like the Space Shuttle, the ISS, or even "regular" rockets.

1960 article by Yuri Artsutanov
proposing the Space Elevator.
(Thanks to Roger Gilbertson)

Space Elevator tether challenge, 2006

The Tether

By far, the tallest hurdle we have to clear on the way to building the Space Elevator is the development of a suitable tether material. The main metric we are concerned about is the strength-to-weight ratio of the material, also known as its specific strength, or tenacity. Steel wire, for example, can be made very strong, but it is also very heavy, so is not a good candidate. Spectra 2000 fiber, in comparison, is a little bit stronger, but what's more important, is about 8 times lighter, making it a much more suitable material, though not quite good enough.

In the chart below, we track the state of the art in advanced materials. The diagonal line is a "reference curve" that depicts a 50% yearly improvement in the specific strength of materials, starting off at what is available today (2005). This reference curve is not a prediction - it is simply something to compare with. As far as material properties go, this is an extremely fast growth curve. Since Carbon Nanotubes are a new class of materials, we do not expect real-life results to follow this smooth gradual curve, but rather advance in larger steps. With a theoretical limit of about 200 GPa-cc/g, the potential of CNTs exceeds our goal, and just like early metals or plastics, the initial improvement in material properties will be very fast.

In the next few years, we will have a more complete picture of whether CNT materials were able to advance at a 50% yearly rate, and whether we encounter fundamental roadblocks that will prevent further advances.

In addition to the reference curve, we plot the following types of data points:

- In Blue, we show numbers measured at the Elevator:2010 competition.
- In Red, we show spec-sheet data for commercial off-the-shelf products.
- In Purple, we show published measurements and analysis results.
- In Green, we show Space Elevator goals.

New!!! Two recent data points, #10 and #11!

The Tether Strength Table

Data Point References

Units and numbers...

The units for measureing specific strength (or tenacity) are confusing - traditionally, people use either GPa-cc/g for the former, and N/Tex for the latter. These two units are the same in fact, and are equal to 1E6 N-m/kg, which is what the pure metric unit should be - force per linear density.

To end confusion once and for all, we propose to name the pure metric unit for both specific strength and tenacity as a Yuri (in honor of Yuri Aatsutanov), and so a tether with a linear tensity of 0.001 kg/m that breaks at 1000 N will have a breaking strength of 1 Mega Yuri.

When building a Space Elevator, the higher the load that the tether can take, the smaller the Taper Ratio, and the lighter the overall Elevator. Beyond a taper ratio of 3, the Space Elevator starts to get very bulky compared to its payloads. Based on this, in order to build the Space Elevator, we need a material we can load with at least 45 MYuri and with a safety factor of 50%, this means a Specific Strength of 65 MYuri. There's no "must have" requirement though - the stronger the material, the less the overall elevator will weigh. With a 100 MYuri material, the Space Elevator tether will weigh less than 1/3 what it would have weighed if constructed from a 50 MYuri material. With a only a 25 MYuri material, the elevator will be heavier by an additional factor of 5.6. Looking at it another way, a 100 MYuri elevator can lift its own weight to orbit in 6 months. A 25 MYuri Space Elevator needs almost 20 years to do the same.

In short - we need to reach the Green numbers on the right side of the graph using macroscopic tethers. To date, theoretical modeling and micro-scale measurements are promising, and the latest results out of Cambridge are very impressive.

We will keep watching!