> 1: Introduction
There appears to be some disparity regarding the nature of the Covenant’s ability to Glass a planet (Both in canon and community). On one hand there is the Halo Reach Data Pads, and a few other sources (such as Halo: Evolutions and Halsey’s Journal), which seem to indicate that they do not actually Glass a planet in totality, while a few of the older books seem to suggest otherwise.
So can the Covenant actually Glass an entire planet within the relatively short time frames described in the older novels or is it just localised and a significantly weaker process as suggested by the Data Pad AI?
Given the scope of the Human-Covenant war, the energy output of Covenant weaponry and the Covenant’s own energy and logistical limitations, there is more than sufficient evidence and reason to believe that the answer is in fact no, despite what the limited first hand accounts of certain characters may say. (This word “limited” is important later on)
> 2: Reasoning
The sole reason which initially gave rise to this idea is the conclusion drawn by the Data Pad AI in that it apparently takes 1 Covenant ship (CCS class) 15 seconds to Glass one acre of land. [1] With that ratio, it takes 30 years for 2000 Covenant ships to Glass an Earth sized planet.
From this, other reasons become apparent.
Firstly, that statement implies that there are 2000 Covenant ships over one planet for 30 years. Given that sort of logistical requirement, it is hard to imagine that the Covenant possesses anywhere near the number of ships required to Glass an entire planet -multiple planets- and wage a multi-system war all at once within the space of 27 years. [2] Furthermore, the rate at which colonies were supposedly Glassed is too quick to support the idea. [2] It would imply that they had much greater than 2000 ships over each colony attacked, or that they could discharge massive amounts of energy in a small space of time which would make them absolutely undefeatable in space. [1] The former is unfeasible, and the latter is not true at all.
The Covenant do not have enough ships to Glass a planet in a space of time that is less than or equal to (or anywhere near, actually) 30 years [2]. There is no reason to take up the assumption, like some people have (E.g. Halopedia), that the Covenant fleet was “many times larger than anticipated” to the extent required, and so there is no reason to assume that the required number of ships came along to do the job quicker. In order to do it in one week (As some people, along with Halopedia, still think is possible. Reach’s glassing was probably the primary source of this idea), the Covenant would need 3.12 million vessels over one colony; a number that they do not have. [3]
> 3: Evidence and reasoning
[1] - So where does this come from, this whole idea about “15 seconds to Glass 1 acre”?
> Data Pad 10
> [^] Importantly, the Covenant does not possess the capacity to accomplish ‘glassing’ on a global scale and wage a multisystem war simultaneously. This is reinforced by hard data regarding their capabilities revealed during fleet engagements with the UNSC. A single Covenant capital ship (CCS-class) is capable of ‘glassing’ approximately one acre of a planet’s surface after an average of fifteen seconds of sustained fire. Understandably this action takes considerably less time when applied to open desert, and considerably longer when applied to deep ocean (> 1.8 km) [^]
The underlined part. Now, how can that be assumed? How do they know this?
Firstly, consider the weapon that is used primarily as the main tool for Glassing. The Energy Projector. It is seen being used again and again, e.g. The Return animated version, Halo 3: Floodgate, Halo 3 ODST: Coastal Highway, Halo Wars Intro, Halo Reach: New Alexandria, etc. This weapon is also used in fleet engagements. It is also in fleet engagements that the determination of the Covenant’s Glassing abilities were found. This weapon, whilst powerful in its own right, is either one of the following:
1 - Insufficient energy output to actually Glass an acre any quicker than 15 seconds.
2 - Poor functionality in that it can only be fired for short durations, followed by a recharge time. Thus the 15 seconds. So even though the Energy Projector’s output may be sufficient to glass an Acre in, let us say 1 second, it may have a cool-down period of 14 seconds thus your 15.
We know from Halo 3 ODST: Coastal Highway that point 2 is not true, leaving only point 1. We see that it can be used for an extended duration. As for point 1 then, the glassing beam has to cross through several kilometres of atmosphere, so by the time it reaches the ground it is “cooler”, unlike in the vacuum of space where there is no interference. That will not account for all of it though. Against ships, it is made into a needle thin energy stream (Battle of Reach), and so is far more potent. When Glassing however, it has a significantly larger cross-section. That means the same energy over more area, decreasing its effectiveness. It is like a 10W tungsten bulb. It is not very bright because its energy is being output in all directions, or in other words it has a low light intensity. However, if you take that 10W and pump it out via a laser and it is a very different story. That 10W output becomes a highly focused and coherent beam with a very high intensity.