The Times Australia
The Times World News

.

The BOLT II hypersonic flight test could bring superfast global travel a step closer

  • Written by Chris James, ARC DECRA Fellow, Centre for Hypersonics, School of Mechanical and Mining Engineering, The University of Queensland
The BOLT II hypersonic flight test could bring superfast global travel a step closer

The BOLT II hypersonic flight experiment will launch tonight from NASA’s Wallops Test Flight Facility[1] in Virginia.

Hypersonic vehicles, which can fly much faster than passenger jets, would allow passengers to go from Sydney to Los Angeles, for instance, in just a couple of hours.

They could also offer more flexible options for launching payloads into space than conventional rockets and their speed and manoeuvrability mean they have a range of potential tactical military uses too.

Russia and China already claim to have operating hypersonic missiles[2], but hypersonic passenger aviation is still a dream rather than reality.

Read more: Hypersonic missiles are fuelling fears of a new superpower arms race[3]

Nevertheless, several types of hypersonic vehicles already exist, including rockets, planetary entry vehicles such as SpaceX’s Dragon capsule[4] and intercontinental ballistic missiles.

What is hypersonic flight?

Hypersonic flight is faster than supersonic flight – the latter term, by definition, means faster than the speed of sound.

To break the sound barrier – and surpass “Mach 1” – you need to travel faster than about 1,235km per hour, or a kilometre in just under 3 seconds. Mach 2 is twice as fast, and so on.

There is no clearly defined Mach number that marks the boundary between supersonic and hypersonic flight. But Mach 5[5] is generally taken by aerospace engineers to be where hypersonic speed begins.

Hypersonic travel presents a few extra problems that aren’t encountered at more pedestrian speeds. Chief among these is the fact that the air flow over the vehicle causes so much friction the outside of the craft can exceed 1,000℃.

Like all aircraft, flying depends on not having too much mass on board. So specialist materials, either high-temperature ceramics or “ablative” materials that slowly burn away during flight[6], are required on the outside of vehicles to insulate the craft against this heat and still be light enough to fly.

Hypersonic engines, called scramjets (supersonic combustion ramjets), need to burn fuel in a supersonic air flow, which is very complicated.

Artist’s impression of the Boeing X-51A Waverider, a scramjet powered hypersonic test vehicle. U.S. Air Force

Another persistent issue is that hypersonic flight is difficult to model accurately, because of the interplay of various different physical effects that come into play at extreme speeds.

So if you want to understand everything together, you have to do real flight tests such as today’s launch. But these are expensive and technically demanding.

Read more: The race to hypersonic speed: will air passengers feel the benefits?[7]

Testing boundaries

One of the trickiest hypersonic problems is predicting something called the “boundary layer transition location”.

When an aircraft flies through the air, a thin layer of air forms around its surface and is dragged along with the vehicle.

This “boundary layer” is very important, as most of the heating happens here, along with a significant portion of the drag forces that try to slow down the vehicle.

As this boundary layer grows along the vehicle’s length, it will eventually “transition” from the calm “laminar” flow near the leading edge of the vehicle, to violent “turbulent” flow further downstream.

Gas flow transitioning from laminar, transitional (in between) and then turbulent on a flat plate. David L. Chandler, MIT News Office

While we understand what leads to this “boundary layer transition”, we can’t perfectly predict it, especially at hypersonic speeds.

The problem is that predicting the boundary layer transition location accurately is very important for designing hypersonic vehicles. In most cases, turbulent flow is bad. It greatly increases both heating and drag.

Uncertainty in where the flow will be turbulent is a major issue, as large heating and drag uncertainties make some vehicle designs inefficient or completely unfeasible.

BOLT II: a new transition flight experiment

BOLT (short for Boundary Layer Transition) was a US$6 million[8] hypersonic flight test that launched in June 2021 from Esrange Space Center in northern Sweden to study boundary layer transition.

But it failed to reach hypersonic speeds, after problems with its rocket launch mechanism.

BOLT II (this time short for Boundary Layer Transition and Turbulence) is the next planned flight in the program, with a similar budget but a larger vehicle to ensure more flow turbulence can be studied[9].

Both the BOLT and BOLT II vehicles have a complex, swept geometry with a concave surface to represent a real hypersonic vehicle[10]. The aim is to produce complex, real-world data that engineers and scientists can use to improve their models for predicting transition on hypersonic vehicles.

A separate experiment is run on each side of the vehicle, with one “smooth” side and one “rough” side[11]. The flow running length along the vehicle is 1 metre[12], slightly larger than the original BOLT vehicle.

BOLT II will be launched on a suborbital trajectory by a two-stage sounding rocket[13]. During its ascent, it is planned to reach Mach 6, where an ascent flight experiment will occur[14]. It will turn over in space and then re-enter the atmosphere, before performing a descent experiment at Mach 5.5[15].

BOLT II is a fully autonomous vehicle and it has more than 400 sensors and instruments mounted onboard[16] to capture data about the flow environment during the experiments.

Assuming that BOLT II’s planned trajectory will be similar to the planned original BOLT flight trajectory, BOLT II will reach a maximum altitude of around 281km[17]. The whole mission will be over in less than 10 minutes after launch[18].

The original BOLT flight vehicle before testing. Air Force Office of Scientific Research/Johns Hopkins APL

Where to from here?

To develop the hypersonic vehicles of the future, we need to properly understand how to predict boundary layer transition on realistic vehicle shapes and what the minute effects of turbulent flow on hypersonic vehicles are. Data from the BOLT II flight experiment will help do just that.

Read more: Sydney to London in an hour? The future of hypersonic air travel[19]

The launch will be livestreamed on the NASA Wallops Youtube channel[20], so we’ll know straight away if the flight is a success or not. Assuming it is, in the coming years we will see many scientific papers published on the breakthroughs from this significant experiment.

The ability to accurately predict hypersonic boundary layer transmission will bring us much closer to hypersonic passenger flight one day. NASA’s planned NASP hypersonic space-plane was cancelled in the 1990s, partly due to the inability to accurately predict its transition location[21]. Hopefully, soon we can move past that.

However, many issues will still remain. Air-breathing hypersonic engines are still in their infancy; the materials used to shield hypersonic vehicles are very expensive; and the design of hypersonic vehicles is still very complicated. Companies like Australia’s own Hypersonix, which aims to use an air-breathing hypersonic vehicle to launch small payloads into orbit[22], will hopefully bring us closer to making the hypersonic flight dream a reality.

References

  1. ^ tonight from NASA’s Wallops Test Flight Facility (www.afrl.af.mil)
  2. ^ operating hypersonic missiles (theconversation.com)
  3. ^ Hypersonic missiles are fuelling fears of a new superpower arms race (theconversation.com)
  4. ^ Dragon capsule (www.spacex.com)
  5. ^ Mach 5 (www.grc.nasa.gov)
  6. ^ either high-temperature ceramics or “ablative” materials that slowly burn away during flight (www.af.mil)
  7. ^ The race to hypersonic speed: will air passengers feel the benefits? (theconversation.com)
  8. ^ US$6 million (aerospaceamerica.aiaa.org)
  9. ^ larger vehicle to ensure more flow turbulence can be studied (aerospaceamerica.aiaa.org)
  10. ^ complex, swept geometry with a concave surface to represent a real hypersonic vehicle (arc.aiaa.org)
  11. ^ one “smooth” side and one “rough” side (arc.aiaa.org)
  12. ^ 1 metre (arc.aiaa.org)
  13. ^ two-stage sounding rocket (www.afrl.af.mil)
  14. ^ Mach 6, where an ascent flight experiment will occur (arc.aiaa.org)
  15. ^ descent experiment at Mach 5.5 (arc.aiaa.org)
  16. ^ more than 400 sensors and instruments mounted onboard (www.afrl.af.mil)
  17. ^ maximum altitude of around 281km (doi.org)
  18. ^ less than 10 minutes after launch (doi.org)
  19. ^ Sydney to London in an hour? The future of hypersonic air travel (theconversation.com)
  20. ^ NASA Wallops Youtube channel (www.youtube.com)
  21. ^ accurately predict its transition location (arc.aiaa.org)
  22. ^ air-breathing hypersonic vehicle to launch small payloads into orbit (hypersonix.com.au)

Read more https://theconversation.com/the-bolt-ii-hypersonic-flight-test-could-bring-superfast-global-travel-a-step-closer-179556

Times Magazine

Headless CMS in Digital Twins and 3D Product Experiences

Image by freepik As the metaverse becomes more advanced and accessible, it's clear that multiple sectors will use digital twins and 3D product experiences to visualize, connect, and streamline efforts better. A digital twin is a virtual replica of ...

The Decline of Hyper-Casual: How Mid-Core Mobile Games Took Over in 2025

In recent years, the mobile gaming landscape has undergone a significant transformation, with mid-core mobile games emerging as the dominant force in app stores by 2025. This shift is underpinned by changing user habits and evolving monetization tr...

Understanding ITIL 4 and PRINCE2 Project Management Synergy

Key Highlights ITIL 4 focuses on IT service management, emphasising continual improvement and value creation through modern digital transformation approaches. PRINCE2 project management supports systematic planning and execution of projects wit...

What AI Adoption Means for the Future of Workplace Risk Management

Image by freepik As industrial operations become more complex and fast-paced, the risks faced by workers and employers alike continue to grow. Traditional safety models—reliant on manual oversight, reactive investigations, and standardised checklist...

From Beach Bops to Alpine Anthems: Your Sonos Survival Guide for a Long Weekend Escape

Alright, fellow adventurers and relaxation enthusiasts! So, you've packed your bags, charged your devices, and mentally prepared for that glorious King's Birthday long weekend. But hold on, are you really ready? Because a true long weekend warrior kn...

Effective Commercial Pest Control Solutions for a Safer Workplace

Keeping a workplace clean, safe, and free from pests is essential for maintaining productivity, protecting employee health, and upholding a company's reputation. Pests pose health risks, can cause structural damage, and can lead to serious legal an...

The Times Features

Prefab’s Second Life: Why Australia’s Backyard Boom Needs a Circular Makeover

The humble granny flat is being reimagined not just as a fix for housing shortages, but as a cornerstone of circular, factory-built architecture. But are our systems ready to s...

Melbourne’s Burglary Boom: Break-Ins Surge Nearly 25%

Victorian homeowners are being warned to act now, as rising break-ins and falling arrest rates paint a worrying picture for suburban safety. Melbourne residents are facing an ...

Exploring the Curriculum at a Modern Junior School in Melbourne

Key Highlights The curriculum at junior schools emphasises whole-person development, catering to children’s physical, emotional, and intellectual needs. It ensures early year...

Distressed by all the bad news? Here’s how to stay informed but still look after yourself

If you’re feeling like the news is particularly bad at the moment, you’re not alone. But many of us can’t look away – and don’t want to. Engaging with news can help us make ...

The Role of Your GP in Creating a Chronic Disease Management Plan That Works

Living with a long-term condition, whether that is diabetes, asthma, arthritis or heart disease, means making hundreds of small decisions every day. You plan your diet against m...

Troubleshooting Flickering Lights: A Comprehensive Guide for Homeowners

Image by rawpixel.com on Freepik Effectively addressing flickering lights in your home is more than just a matter of convenience; it's a pivotal aspect of both home safety and en...