The_Solar_Oracle t1_j8qhuf2 wrote on February 16, 2023 at 5:30 AM

Reply to comment by urmomaisjabbathehutt in After a decade in development, Japan’s H3 rocket is ready for its debut by DoremusJessup

Single stage to orbit is highly unlikely to happen (or at least become common) in the foreseeable future. Even very optimistic concepts have very small payloads for the masses in question, and any weight gained during development could compromise that capacity. Moreover, there's a case to be made against SSTOs given other potential designs.

Reaction Engines Limited 2014 concept detailing the Skylon D1, for instance, has a 325,000 kilogram fully fueled SSTO delivering a 53,500 kilo vehicle (empty) into the lowest possible equatorial orbit with 15,000 kilos of worth of payload. That 53 1/2 ton vehicle is a larger penalty against the payload mass than the STS' Orbiters were, and the payload capacity itself is inferior to modern, partially reusable Falcon 9s. Yes, they're not totally reusable, but one wonders if the savings of reusing that expended mass would be worth the added developmental costs.

If the SABRE engines are not as good as thought or if new features and their extra mass must be added (as had happened in the aftermath of the Falcon 9's initial landing failures), the resulting payload mass reductions would be larger than they would be for multi-stage craft. Hypersonic engine research is also very difficult and very expensive, and that high R&D means there would have to be a significant frequency of flights and low turn around time for the vehicle to be competitive. Additionally, Skylon D1s delivering payloads to higher orbits would invariably rely on independent upper stages that would likely be disposable.

However, as far as plasma jet engines go, the largest bottleneck for them is energy storage. Amusingly, Gerard K. O'Neill's 2081: A Hopeful View of the Human Future had launch vehicles conveniently get around this issue by using Solar Power Satellites as their energy source during airbreathing mode in lieu of storing it all onboard. Not bad for a book published in 1981! While we are currently in want of SPSes, the idea has finally gotten real traction in the last decade with the entities within United States, China and Europe having committed to launching SPS testbeds into orbit in the next few years.

urmomaisjabbathehutt t1_j8r2pt5 wrote on February 16, 2023 at 10:01 AM

that is an interesting resume, thanks

the situation kind of reminds me the issues we have trying to achieve fusion energy, in both cases we know the that phisics work, we know is a desirable outcome but we need to workout the engineering problems

payload size may be an issue with early technology but if we at least manage reliable vehicules for human transportation that is one less problem and lower risk level until we can figure heavy loaders and eventually we are going to need an increased number of people working upthere becoming routine

The_Solar_Oracle t1_j8utuaa wrote on February 17, 2023 at 2:32 AM

>"the situation kind of reminds me the issues we have trying to achieve fusion energy, in both cases we know the that phisics work, we know is a desirable outcome but we need to workout the engineering problems"

Sometimes, engineering problems can themselves be insurmountable or simply not worth implementing. It's not a great feeling, but it's happened in the past and will happened again.

Nonetheless, the low payload capacities of SSTOs are a big risk because there may simply not be a worthwhile market for such small sizes. So many people focus on kilos to Low Earth Orbit while failing to take into account any other factor. It matters very little if you can get 1 kilogram to orbit for mere pennies at a time if no one wants to launch something that small, and a lot of payloads require additional space or higher orbits that any near-future SSTO would be hard pressed to accommodate.