Technological challenges to sending a high altitude balloon to space and orbit from 50 km?

If you want to be above all winds, you have to be above all atmosphere. But you can't get above all atmosphere with a ballon. There is no ballon lighter than a vacuum.

Conventional helium balloons get up to roughly 50 km, which is half way there in terms of altitude but a factor of almost 2,000 away in density.

• There have been hight altitude instrumentation balloons that reach nearly to 50 km.
• There have been demonstrations of ion wind propulsion at sea level at MIT (MIT EAD Airframe Version 2).
• There have been balloons in space, in orbit around Earth: 1, 2 3 (#3 is unanswered)

Suppose a big normal balloon were to loft our special balloon to 50 km where it inflated. What would be the technical challenges to getting it moving and rising up to the Karman line at 100 km or beyond with orbital velocity? Include photovoltaic, solar-thermal, radioisotope or other clever ways to make power and clever propulsion schemes, use state of the art materials and a substantial budget and R&D effort for this admittedly crazy demonstrator mission, and answer:

Question: What are the main technological challenges to sending a high altitude balloon to space and orbit starting from 50 km?

From NASA TM-X-74335/NOAA-S/T 76-1562: U.S. Standard Atmosphere, 1976

Altitude    Pressure    Temperature     Density
(km)       (mbar)         (K)         (kg/m^3)
-------     --------    -----------     -------
50        7.6E-01        271         9.8E-04
100        3.2E-04        195         5.6E-07


For previous thinking in this area and sources of references, see also

• What about reaching orbital speed by the balloon in the upper atmosphere where there is still atmospheric drag? High speed would destroy the balloon when exposed to a very low pressure. Balloons are known for very low speed difference between air and balloon.
– Uwe
Commented Jan 1, 2021 at 5:07
• I think you need to separate "space" and "orbit". Getting to 100km is one challenge, getting up to orbital velocity is an entirely different one. Commented Jan 1, 2021 at 10:43
• @uhoh OK. I understand now. I suspect the hardest part is relatively early on when the balloon is moving at mach 5-10 relative to the local atmosphere. It still needs to support most of its weight by bouyancy and aerodyanmic lift. If much of that comes from bouyancy then it must be large and the surrounding air can't be too thin, but then the drag would be horrendous. If most of it comes from lift, then it's not really a balloon, and either way it needs so much propulsive power that it must be using stored energy and will have limited time. Commented Jan 1, 2021 at 12:27
• You may be interested in JP Aerospace's "Airship to Orbit" project: jpaerospace.com/ATO/ATO.html Commented Jan 5, 2021 at 17:30
• @uhoh I couldn't find a ton of technical details; though there is a PDF on their website which offers a bit more information than the landing page: jpaerospace.com/atohandout.pdf Wikipedia also has a small overview on the concept, though it's mostly sourced from the same PDF: en.wikipedia.org/wiki/JP_Aerospace#Airship_to_Orbit_project Commented Jan 5, 2021 at 19:28